Introduce ViewRoot forwarding input/view events to native

ui/android/view_android.h

Index: ui/android/view_android.h
diff --git a/ui/android/view_android.h b/ui/android/view_android.h
index d05520d514b7ee525f1b85ec78f8fb7ceb1cd04b..3e6e2398c85b13c15a153cb8f0b3621aaf3d73e9 100644
--- a/ui/android/view_android.h
+++ b/ui/android/view_android.h
@@ -22,7 +22,7 @@ class ViewClient;
 class WindowAndroid;
 
 // A simple container for a UI layer.
-// At the root of the hierarchy is a WindowAndroid, when attached.
+// At the root of the hierarchy is a ViewRoot, a subclass of ViewAndroid.
 class UI_ANDROID_EXPORT ViewAndroid {
  public:
   // Stores an anchored view to delete itself at the end of its lifetime
@@ -64,9 +64,9 @@ class UI_ANDROID_EXPORT ViewAndroid {
   // if disconnected.
   virtual WindowAndroid* GetWindowAndroid() const;
 
-  // Returns |ViewRoot| associated with the current ViewAndroid.
-  // Create one if not present.
-  base::android::ScopedJavaLocalRef<jobject> GetViewRoot();
+  // Set the root |WindowAndroid|. This is simply passed up to the root
+  // of the tree i.e. |ViewRoot| where the reference is held.
+  virtual void SetWindowAndroid(WindowAndroid* window);

[boliu, 2017/01/03 19:16:11]

This should not be needed.

First this seems to be a method that should be on ViewRoot only, not View.

For both chrome and webview, WindowAndroid and ViewRoot should be set *together*
everywhere. And the mapping from a ViewRoot to WindowAndroid should never have
to change. This applies to tab reparenting in chrome as well, ie when
reparenting to a new WindowAndroid, should start using a new ViewRoot as well.
So there should be no need for SetWindowAndroid in ViewRoot either.

[Jinsuk Kim, 2017/01/04 10:45:02]

Done. Is this suggestion about the immutable pairing between ViewRoot -
WindowAndroid to make it easy to track their relationship? 

[boliu, 2017/01/04 17:45:10]

Yeah. Also to keep things simple and avoid unnecessary complexity.

[Jinsuk Kim, 2017/01/05 11:03:12]

Acknowledged.

 
   // Used to return and set the layer for this view. May be |null|.
   cc::Layer* GetLayer() const;
@@ -91,9 +91,12 @@ class UI_ANDROID_EXPORT ViewAndroid {
   void UpdateLayerBounds();
 
   // Internal implementation of ViewClient forwarding calls to the interface.
-  void OnPhysicalBackingSizeChanged(int width, int height);
+  void OnPhysicalBackingSizeChangedInternal(int width, int height);

[boliu, 2017/01/03 19:16:11]

the rename is to avoid name collision with ViewRoot, right?

maybe this should be protected then?

[Jinsuk Kim, 2017/01/04 10:45:02]

Done.

 
  protected:
+  // Returns the root of this hierarchy.

[boliu, 2017/01/03 19:16:11]

not quite, returns the ViewRoot of the hierarchy, but null if hierarchy isn't
attached to a ViewRoot

[Jinsuk Kim, 2017/01/04 10:45:02]

Done.

+  virtual ViewAndroid* GetViewRoot();
+
   ViewAndroid* parent_;
 
  private:
@@ -116,12 +119,14 @@ class UI_ANDROID_EXPORT ViewAndroid {
   // should have |ViewRoot| for this ViewAndroid to have one.
   base::android::ScopedJavaLocalRef<jobject> CreateViewRoot();
 
-  bool HasViewRoot();
+  // Checks if this is the root of the view tree. Used to avoid ending up
+  // with multiple roots when modifying a tree.
+  bool IsViewRoot();
 
   std::list<ViewAndroid*> children_;
+
   scoped_refptr<cc::Layer> layer_;
   JavaObjectWeakGlobalRef delegate_;
-  JavaObjectWeakGlobalRef view_root_;
   ViewClient* const client_;
 
   int physical_width_pix_;
@@ -130,8 +135,6 @@ class UI_ANDROID_EXPORT ViewAndroid {
   DISALLOW_COPY_AND_ASSIGN(ViewAndroid);
 };
 
-bool RegisterViewRoot(JNIEnv* env);
-
 }  // namespace ui
 
 #endif  // UI_ANDROID_VIEW_ANDROID_H_