Introduce ViewRoot forwarding input/view events to native

ui/snapshot/snapshot_android.cc

Index: ui/snapshot/snapshot_android.cc
diff --git a/ui/snapshot/snapshot_android.cc b/ui/snapshot/snapshot_android.cc
index 557a325db03b1682b79613561520a3070ea4bfb0..bf07e43f91e632ffe45ea15031fb3ac032a0ad89 100644
--- a/ui/snapshot/snapshot_android.cc
+++ b/ui/snapshot/snapshot_android.cc
@@ -42,8 +42,11 @@ static void MakeAsyncCopyRequest(
   std::unique_ptr<cc::CopyOutputRequest> request =
       cc::CopyOutputRequest::CreateBitmapRequest(callback);
 
+  ViewAndroid view;
+  view.SetWindowAndroid(window);

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

err, this is just wrong..

This code can talk to DisplayAndroidManager directly, so maybe should do that.

So add a DisplayAndroidManager::GetInstance method, which can get the screen and
just downcast it. Then add a method to DisplayAndroidManager that just takes a
WindowAndroid.

This does beg the question, long term, should gfx::NativeWindow be redefined to
ViewRoot. I'm not sure what the answer is though.. whatever is convenient I
guess.

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

I have a problem getting this to build(undefined reference to
'ui::DisplayAndroidManager::GetDisplayNearestWindowAndroid(ui::WindowAndroid*)
const'). Will fix this soon.

[boliu, 2017/01/04 18:58:05]

Need to add UI_ANDROID_EXPORT to DisplayAndroidManager

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

Ah

+
   const display::Display& display =
-      display::Screen::GetScreen()->GetDisplayNearestWindow(window);
+      display::Screen::GetScreen()->GetDisplayNearestWindow(&view);
   float device_scale_factor = display.device_scale_factor();
   gfx::Rect source_rect_in_pixel =
       gfx::ScaleToEnclosingRect(source_rect, device_scale_factor);