Introduce ViewRoot to forward input/view events to native

ui/android/event_handler.h

+// Copyright 2016 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 UI_ANDROID_EVENT_HANDLER_H_
+#define UI_ANDROID_EVENT_HANDLER_H_
+
+#include "base/android/jni_android.h"
+#include "base/android/scoped_java_ref.h"
+#include "ui/android/ui_android_export.h"
+
+namespace ui {
+
+class ViewAndroid;
+
+// A simple container for a UI layer.
+// At the root of the hierarchy is a WindowAndroid, when attached.
+class UI_ANDROID_EXPORT EventHandler {

[boliu, 2016/12/02 23:53:22]

ViewAndroid::GetEventHandler definitely should not be public

Is it possible to not have this in a header at all? Just make all the
java->native calls static so the generator doesn't need a separate header for
the class, then can directly implement things internally in view_android.cc?

[Jinsuk Kim, 2016/12/05 11:07:44]

Removed the class EventHandler and defined the example method static.

+ public:
+  EventHandler(ViewAndroid* view);
+
+  void OnPhysicalBackingSizeChanged(JNIEnv* env,
+      const base::android::JavaParamRef<jobject>& obj,
+      int width,
+      int height);
+
+  int GetPhysicalBackingSizeWidthPix();
+  int GetPhysicalBackingSizeHeightPix();
+
+ private:
+  ui::ViewAndroid* view_;
+
+  int physical_width_pix_;

[boliu, 2016/12/02 23:53:22]

this is a property on ViewAndroid, not handler

this is where the whole ViewAndroid hierarchy comes in, the size needs to be
propagated down the tree, and when a child is added, the size should be
propagated to the child as well

[Jinsuk Kim, 2016/12/05 11:07:44]

Moved the properties to ViewAndroid.

I *think* the size of the new child is being updated already somewhere else when
added. Do you suggest it be done in ViewAndroid::AddChild? 

[boliu, 2016/12/06 00:10:17]

Yes

[Jinsuk Kim, 2016/12/06 07:35:07]

Traced the code and found that child nodes are all added before the first
physical backing size change happens - so it has not been necessary to update
the size to that of the parent so far. Do you believe it will necessary to do
that in the future? I think simply calling child->OnPhysicalBackingSizeChanged()
in AddChild if the parent's size is valid will do the trick.

[boliu, 2016/12/06 19:13:59]

I don't see why not, in the name of correctness. You can avoid propagation
overhead by just returning immediately if nothing actually changed.

[Jinsuk Kim, 2016/12/07 12:36:28]

Done.

+  int physical_height_pix_;
+
+  DISALLOW_COPY_AND_ASSIGN(EventHandler);
+};
+
+bool RegisterEventHandler(JNIEnv* env);
+
+}  // namespace ui
+
+#endif  // UI_ANDROID_EVENT_HANDLER_H_