Introduce ViewRoot forwarding input/view events to native

ui/android/java/src/org/chromium/ui/base/ViewRoot.java

Index: ui/android/java/src/org/chromium/ui/base/ViewRoot.java
diff --git a/ui/android/java/src/org/chromium/ui/base/ViewRoot.java b/ui/android/java/src/org/chromium/ui/base/ViewRoot.java
index c224e8e3ed8c9cdfd31b3ed2e783e090ea42a4e7..4697b199b231314c57b28d6cc3d187dd56b131b0 100644
--- a/ui/android/java/src/org/chromium/ui/base/ViewRoot.java
+++ b/ui/android/java/src/org/chromium/ui/base/ViewRoot.java
@@ -9,10 +9,6 @@ import org.chromium.base.annotations.JNINamespace;
 
 /**
  * Class used to forward view, input events down to native.
- *
- * TODO(jinsukkim): Add its native counterpart inheriting from ViewAndroid
- *     so that it will act as a root of ViewAndroid tree. It effectively
- *     replaces WindowAndroid in terms of the role.
  */
 @JNINamespace("ui")
 public class ViewRoot {
@@ -20,13 +16,12 @@ public class ViewRoot {
     // the native instance is alive.
     private long mNativeView;
 
-    @CalledByNative
-    private static ViewRoot create(long nativeView) {
-        return new ViewRoot(nativeView);
+    public static ViewRoot create(WindowAndroid window) {

[boliu, 2017/01/04 18:58:06]

return null if window is null? or could throw an except too..

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

Done. Chose to throw an exception.

+        return new ViewRoot(window);
     }
 
-    private ViewRoot(long nativeView) {
-        mNativeView = nativeView;
+    private ViewRoot(WindowAndroid window) {
+        mNativeView = nativeInit(window == null ? 0 : window.getNativePointer());
     }
 
     /**
@@ -41,10 +36,16 @@ public class ViewRoot {
     }
 
     @CalledByNative
+    private long getNativePtr() {
+        return mNativeView;
+    }
+
+    @CalledByNative
     private void onDestroyNativeView() {
         mNativeView = 0;
     }
 
-    private static native void nativeOnPhysicalBackingSizeChanged(long viewAndroid,
+    private native long nativeInit(long windowNativePointer);
+    private native void nativeOnPhysicalBackingSizeChanged(long nativeViewRoot,
             int width, int height);
 }