URLPattern: Canonicalize pattern encoding.

This CL adds an encoding callback to liburlpattern::Parse().  The
parse will invoke the given callback for plaintext parts of the pattern
to validate and encode the characters.  This callback mechanism is then
used to apply the chromium url canonicalization code for each component
pattern.

There are a couple of behaviors in the canonicalizer that do not play
well with this approach that the CL works around:

1. The port canonicalizer will replace an exact default port with the
   empty string.  Since the liburlpattern::Parse() callback is invoked
   for partial values this CL instead implements this canoncilization
   separately before pattern compilation.
2. The URL canonicalizer will prepend a leading `/` character if there
   isn't one.  Again, this behavior does not make sense when operating
   on partial values.  Therefore this CL exposes the internal partial
   path canonicalization routine so that we can use it in URLPattern.

In addition, this CL removes a DCHECK from url's DoPartialPath() that
asserted there was always a character preceding a dot.  The DCHECK has
had a runtime check checking the same behavior since 2013 so it seems
safe to remove the DCHECK.  And in this case we want to be able to
run the canonicalize partial paths that do start with dots.

The CL adds a number of additional WPT test cases validating the new
canonicalization behavior.

The behavior in this test has been discussed in this spec issue:

whatwg/urlpattern#33

Bug: 1141510
Change-Id: I388be5d0cc57b125d44465b283050df5ed0b5321
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2720702
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Commit-Queue: Ben Kelly <wanderview@chromium.org>
Cr-Commit-Position: refs/heads/master@{#860399}

urlpattern/resources/urlpatterntestdata.json

@@ -985,6 +985,14 @@
       "username": { "input": "caf%C3%A9", "groups": {}}
     }
   },
+  {
+    "pattern": { "username": "café" },
+    "input": { "username" : "café" },
+    "expected": {
+      "input": { "username" : "café" },
+      "username": { "input": "caf%C3%A9", "groups": {}}
+    }
+  },
   {
     "pattern": { "username": "caf%c3%a9" },
     "input": { "username" : "café" },
@@ -998,6 +1006,14 @@
       "password": { "input": "caf%C3%A9", "groups": {}}
     }
   },
+  {
+    "pattern": { "password": "café" },
+    "input": { "password" : "café" },
+    "expected": {
+      "input": { "password" : "café" },
+      "password": { "input": "caf%C3%A9", "groups": {}}
+    }
+  },
   {
     "pattern": { "password": "caf%c3%a9" },
     "input": { "password" : "café" },
@@ -1011,6 +1027,14 @@
       "hostname": { "input": "xn--caf-dma.com", "groups": {}}
     }
   },
+  {
+    "pattern": { "hostname": "café.com" },
+    "input": { "hostname" : "café.com" },
+    "expected": {
+      "input": { "hostname" : "café.com" },
+      "hostname": { "input": "xn--caf-dma.com", "groups": {}}
+    }
+  },
   {
     "pattern": { "port": "" },
     "input": { "protocol": "http", "port": "80" },
@@ -1020,6 +1044,35 @@
       "port": { "input": "", "groups": {}}
     }
   },
+  {
+    "pattern": { "protocol": "http", "port": "80" },
+    "input": { "protocol": "http", "port": "80" },
+    "expected": {
+      "input": { "protocol": "http", "port": "80" },
+      "protocol": { "input": "http", "groups": {}},
+      "port": { "input": "", "groups": {}}
+    }
+  },
+  {
+    "pattern": { "protocol": "http", "port": "80{20}?" },
+    "input": { "protocol": "http", "port": "80" },
+    "expected": null
+  },
+  {
+    "pattern": { "protocol": "http", "port": "80 " },
+    "input": { "protocol": "http", "port": "80" },
+    "error": true
+  },
+  {
+    "pattern": { "port": "80" },
+    "input": { "protocol": "http", "port": "80" },
+    "expected": null
+  },
+  {
+    "pattern": { "protocol": "http{s}?", "port": "80" },
+    "input": { "protocol": "http", "port": "80" },
+    "expected": null
+  },
   {
     "pattern": { "port": "80" },
     "input": { "port": "80" },
@@ -1057,6 +1110,14 @@
       "pathname": { "input": "/caf%C3%A9", "groups": {}}
     }
   },
+  {
+    "pattern": { "pathname": "/café" },
+    "input": { "pathname": "/café" },
+    "expected": {
+      "input": { "pathname": "/café" },
+      "pathname": { "input": "/caf%C3%A9", "groups": {}}
+    }
+  },
   {
     "pattern": { "pathname": "/caf%c3%a9" },
     "input": { "pathname": "/café" },
@@ -1077,6 +1138,25 @@
       "pathname": { "input": "/foo/bar", "groups": {}}
     }
   },
+  {
+    "pattern": { "pathname": "/foo/../bar" },
+    "input": { "pathname": "/bar" },
+    "expected": {
+      "input": { "pathname": "/bar" },
+      "pathname": { "input": "/bar", "groups": {}}
+    }
+  },
+  {
+    "pattern": { "pathname": "./foo/bar", "baseURL": "https://example.com" },
+    "input": { "pathname": "foo/bar", "baseURL": "https://example.com" },
+    "expected": {
+      "input": { "pathname": "foo/bar", "baseURL": "https://example.com" },
+      "exactly_empty_components": [ "username", "password", "port" ],
+      "protocol": { "input": "https", "groups": {}},
+      "hostname": { "input": "example.com", "groups": {}},
+      "pathname": { "input": "/foo/bar", "groups": {}}
+    }
+  },
   {
     "pattern": { "pathname": "foo/bar" },
     "input": "https://example.com/foo/bar",
@@ -1112,6 +1192,14 @@
       "search": { "input": "q=caf%C3%A9", "groups": {}}
     }
   },
+  {
+    "pattern": { "search": "q=café" },
+    "input": { "search": "q=café" },
+    "expected": {
+      "input": { "search": "q=café" },
+      "search": { "input": "q=caf%C3%A9", "groups": {}}
+    }
+  },
   {
     "pattern": { "search": "q=caf%c3%a9" },
     "input": { "search": "q=café" },
@@ -1125,6 +1213,14 @@
       "hash": { "input": "caf%C3%A9", "groups": {}}
     }
   },
+  {
+    "pattern": { "hash": "café" },
+    "input": { "hash": "café" },
+    "expected": {
+      "input": { "hash": "café" },
+      "hash": { "input": "caf%C3%A9", "groups": {}}
+    }
+  },
   {
     "pattern": { "hash": "caf%c3%a9" },
     "input": { "hash": "café" },