Revert "Flatten ModuleTreeLinker"

This reverts commit 5a168df.

Reason for revert: find-it says this bloke the linux build

Original change's description:
> Flatten ModuleTreeLinker
> 
> 1. This CL applies the spec change by
> whatwg/html#2971.
> Since [1], the code has already been behaving like the spec PR 2971, and this CL
> makes the code align with PR 2971 more completely, by removing AncestorList
> and adding spec comments.
> 
> 2. This CL also flattens the code structure of ModuleTreeLinker, which is
> enabled by the spec PR 2971, to make the code simpler to make further
> optimizations easy.
> That is, instead of creating a ModuleTreeLinker for each module script
> (i.e. for each "fetch the descendants" call) in a module graph, this CL
> creates a single ModuleTreeLinker that corresponds to a top-level module graph
> script.
> 
> Most of fetching-related classes/methods, including
> - ModuleTreeLinker::DependencyModuleClient
> - ModuleTreeLinker::FetchDescendants()
> - ModuleTreeLinker::NotifyOneDescendantFinished()
> are merged into the single method NotifyModuleLoadFinished() that implements
> the main body of "fetch the descendants" and
> "internal module script graph fetching procedure".
> 
> This also removes ModuleTreeReachedUrlSet and instead uses HashSet<KURL>
> directly, as we no longer have to share it across multiple ModuleTreeLinkers.
> Modulator::FetchTreeInternal() is removed as we no longer create
> ModuleTreeLinkers for subtree fetching via Modulator.
> 
> 3. This CL applies a part of
> whatwg/html#2991, particularly introduces
> FindFirstParseError() that corresponds to "find the first parse error" and
> use it to find the error to be reported, instead of propagating errors
> based on Step 6.1 and 6.2 of "fetch the descendants".
> 
> (*) In some subtle cases, this might cause behavior changes in error reporting,
> but these changes shouldn't be significant, because anyway the spec before
> PR 2991 (and thus the previous implementation) behaves nondeterministically
> in some similarly subtle cases.
> 
> This CL is an intermediate step to apply spec PRs 2971 and 2991.
> This CL refactors largely ModuleTreeLinker with keeping the existing behavior
> mostly (except for (*)), and subsequent CLs will apply the behavior changes
> and remaining code structure changes introduced by PR 2991.
> 
> Bug: 763597
> Change-Id: I0ef38c5ebf462fa7f02093f1725ea0014b80585d
> Reviewed-on: https://chromium-review.googlesource.com/583552
> Commit-Queue: Hiroshige Hayashizaki <hiroshige@chromium.org>
> Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#503034}

TBR=hiroshige@chromium.org,ksakamoto@chromium.org,kouhei@chromium.org,nhiroki@chromium.org

Change-Id: I297bca8d91c91f49e4ef1e46a01a1af90a7e67ef
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 763597
Reviewed-on: https://chromium-review.googlesource.com/674784
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Commit-Queue: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#503059}

third_party/WebKit/Source/core/dom/AncestorList.h

@@ -0,0 +1,22 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef AncestorList_h
+#define AncestorList_h
+
+#include "platform/weborigin/KURL.h"
+#include "platform/weborigin/KURLHash.h"
+#include "platform/wtf/HashSet.h"
+
+namespace blink {
+
+// Maps to "ancestor list" concept referenced in multiple module script
+// algorithms.
+// Example:
+// https://html.spec.whatwg.org/#internal-module-script-graph-fetching-procedure
+using AncestorList = HashSet<KURL>;
+
+}  // namespace blink
+
+#endif

third_party/WebKit/Source/core/dom/BUILD.gn

@@ -16,6 +16,7 @@ blink_core_sources("dom") {
     "AccessibleNode.h",
     "AccessibleNodeList.cpp",
     "AccessibleNodeList.h",
+    "AncestorList.h",
     "AnimationWorkletProxyClient.cpp",
     "AnimationWorkletProxyClient.h",
     "Attr.cpp",

third_party/WebKit/Source/core/dom/Modulator.h

@@ -7,6 +7,7 @@
 
 #include "bindings/core/v8/ScriptModule.h"
 #include "core/CoreExport.h"
+#include "core/dom/AncestorList.h"
 #include "platform/bindings/ScriptWrappable.h"
 #include "platform/bindings/V8PerContextData.h"
 #include "platform/heap/Handle.h"
@@ -23,6 +24,7 @@ class ModuleScript;
 class ModuleScriptFetcher;
 class ModuleScriptFetchRequest;
 class ModuleScriptLoaderClient;
+class ModuleTreeReachedUrlSet;
 class ScriptModuleResolver;
 class ScriptState;
 class ScriptValue;
@@ -87,6 +89,13 @@ class CORE_EXPORT Modulator : public GarbageCollectedFinalized<Modulator>,
   virtual void FetchTree(const ModuleScriptFetchRequest&,
                          ModuleTreeClient*) = 0;
 
+  // https://html.spec.whatwg.org/#internal-module-script-graph-fetching-procedure
+  virtual void FetchTreeInternal(const ModuleScriptFetchRequest&,
+                                 const AncestorList&,
+                                 ModuleGraphLevel,
+                                 ModuleTreeReachedUrlSet*,
+                                 ModuleTreeClient*) = 0;
+
   // Asynchronously retrieve a module script from the module map, or fetch it
   // and put it in the map if it's not there already.
   // https://html.spec.whatwg.org/#fetch-a-single-module-script

third_party/WebKit/Source/core/dom/ModulatorImplBase.cpp

@@ -56,18 +56,30 @@ void ModulatorImplBase::FetchTree(const ModuleScriptFetchRequest& request,
   // its argument.
   DCHECK(request.GetReferrer().IsNull());
 
-  // We ensure module-related code is not executed without the flag.
-  // https://crbug.com/715376
-  CHECK(RuntimeEnabledFeatures::ModuleScriptsEnabled());
-
-  tree_linker_registry_->Fetch(request, this, client);
+  AncestorList empty_ancestor_list;
+  FetchTreeInternal(request, empty_ancestor_list,
+                    ModuleGraphLevel::kTopLevelModuleFetch, nullptr, client);
 
   // Step 2. When the internal module script graph fetching procedure
   // asynchronously completes with result, asynchronously complete this
   // algorithm with result.
   // Note: We delegate to ModuleTreeLinker to notify ModuleTreeClient.
 }
 
+void ModulatorImplBase::FetchTreeInternal(
+    const ModuleScriptFetchRequest& request,
+    const AncestorList& ancestor_list,
+    ModuleGraphLevel level,
+    ModuleTreeReachedUrlSet* reached_url_set,
+    ModuleTreeClient* client) {
+  // We ensure module-related code is not executed without the flag.
+  // https://crbug.com/715376
+  CHECK(RuntimeEnabledFeatures::ModuleScriptsEnabled());
+
+  tree_linker_registry_->Fetch(request, ancestor_list, level, this,
+                               reached_url_set, client);
+}
+
 void ModulatorImplBase::FetchDescendantsForInlineScript(
     ModuleScript* module_script,
     ModuleTreeClient* client) {

third_party/WebKit/Source/core/dom/ModulatorImplBase.h

@@ -18,6 +18,7 @@ class ExecutionContext;
 class ModuleMap;
 class ModuleScriptLoaderRegistry;
 class ModuleTreeLinkerRegistry;
+class ModuleTreeReachedUrlSet;
 class ScriptState;
 class WebTaskRunner;
 
@@ -50,6 +51,11 @@ class ModulatorImplBase : public Modulator {
   void FetchTree(const ModuleScriptFetchRequest&, ModuleTreeClient*) override;
   void FetchDescendantsForInlineScript(ModuleScript*,
                                        ModuleTreeClient*) override;
+  void FetchTreeInternal(const ModuleScriptFetchRequest&,
+                         const AncestorList&,
+                         ModuleGraphLevel,
+                         ModuleTreeReachedUrlSet*,
+                         ModuleTreeClient*) override;
   void FetchSingle(const ModuleScriptFetchRequest&,
                    ModuleGraphLevel,
                    SingleModuleClient*) override;

third_party/WebKit/Source/core/loader/BUILD.gn

@@ -94,6 +94,7 @@ blink_core_sources("loader") {
     "modulescript/ModuleTreeLinker.h",
     "modulescript/ModuleTreeLinkerRegistry.cpp",
     "modulescript/ModuleTreeLinkerRegistry.h",
+    "modulescript/ModuleTreeReachedUrlSet.h",
     "modulescript/WorkletModuleScriptFetcher.cpp",
     "modulescript/WorkletModuleScriptFetcher.h",
     "private/FrameClientHintsPreferencesContext.cpp",