Introduce ViewRoot to forward input/view events to native

ui/android/window_android.h

Index: ui/android/window_android.h
diff --git a/ui/android/window_android.h b/ui/android/window_android.h
index 05279ced4c92a2a9e8827b15c67e0c94187a9e11..2ca1bf4409a7cc45ef8fc94d44edddf849b174db 100644
--- a/ui/android/window_android.h
+++ b/ui/android/window_android.h
@@ -74,6 +74,8 @@ class UI_ANDROID_EXPORT WindowAndroid : public ViewAndroid {
                          const base::android::JavaParamRef<jobject>& obj);
   void OnActivityStarted(JNIEnv* env,
                          const base::android::JavaParamRef<jobject>& obj);
+  base::android::ScopedJavaLocalRef<jobject> GetEventHandler(JNIEnv* env,
+      const base::android::JavaParamRef<jobject>& obj);
 
   // Return whether the specified Android permission is granted.
   bool HasPermission(const std::string& permission);
@@ -89,6 +91,7 @@ class UI_ANDROID_EXPORT WindowAndroid : public ViewAndroid {
   ~WindowAndroid() override;
 
   // ViewAndroid overrides.
+  using ViewAndroid::GetEventHandler;
   WindowAndroid* GetWindowAndroid() const override;
 
   // The ID of the display that this window belongs to.