Unset mComponentScope in the root ComponentContext.

Summary:
When a `ComponentTree` is initialized with a `ComponentContext` from another Component (from another tree) the global key of the root component is generated in context of a component which is outside the tree. This is generally `null`.

In such a case when a state update is dispatched, and the framework tries to generate the global key for the root component. The root component (which has a non null parent in this case) will ask its parent to generate a global key.

Now the **falsy** parent components child counters haven’t been reset so it will check that this is a new instance of the same component and deduplicate the global key (i.e. append !n). This changes the global keys for all descendants components.

In some cases it can trigger a new state update and the cycle repeat over and over again.

Reviewed By: davidaurelio

Differential Revision: D15363542

fbshipit-source-id: bea8923e7087dbdedb430b3c1af5a47e688e4193

litho-core/src/main/java/com/facebook/litho/ComponentContext.java

@@ -524,6 +524,7 @@ static ComponentContext withComponentTree(ComponentContext context, ComponentTre
     ComponentContext componentContext =
         new ComponentContext(context, new StateHandler(), null, null, null);
     componentContext.mComponentTree = componentTree;
+    componentContext.mComponentScope = null;
     componentContext.mLayoutStateFuture = null;
 
     return componentContext;

litho-it/src/test/java/com/facebook/litho/ComponentTreeTest.java

@@ -165,6 +165,16 @@ public void testCreate() {
     Assert.assertFalse(componentTreeHasSizeSpec(componentTree));
   }
 
+  @Test
+  public void testCreate_ContextIsNotScoped() {
+    ComponentContext scopedContext =
+        ComponentContext.withComponentScope(mContext, Row.create(mContext).build());
+    ComponentTree componentTree = ComponentTree.create(scopedContext, mComponent).build();
+
+    ComponentContext c = Whitebox.getInternalState(componentTree, "mContext");
+    Assert.assertNull(c.getComponentScope());
+  }
+
   @Test
   public void testSetSizeSpec() {
     ComponentTree componentTree =
@@ -202,6 +212,25 @@ public void testSetSizeSpecAsync() {
     postSizeSpecChecks(componentTree, "mBackgroundLayoutState");
   }
 
+  @Test
+  public void testLayoutState_ContextIsNotScoped() {
+    ComponentContext scopedContext =
+        ComponentContext.withComponentScope(mContext, Row.create(mContext).build());
+    Component root = Column.create(scopedContext).build();
+
+    ComponentTree componentTree = ComponentTree.create(scopedContext, root).build();
+
+    componentTree.setSizeSpecAsync(mWidthSpec, mHeightSpec);
+
+    mLayoutThreadShadowLooper.runOneTask();
+
+    LayoutState layoutState = getInternalState(componentTree, "mBackgroundLayoutState");
+    ComponentContext c = getInternalState(componentTree, "mContext");
+    assertThat(c).isNotEqualTo(scopedContext);
+    Assert.assertNull(c.getComponentScope());
+    assertThat(layoutState.getRootComponent().getScopedContext()).isNotEqualTo(scopedContext);
+  }
+
   @Test
   public void testSetSizeSpecAsyncThenSyncBeforeRunningTask() {
     ComponentTree componentTree =