Introduce ViewRoot to forward input/view events to native

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

Index: ui/android/java/src/org/chromium/ui/base/ViewAndroidDelegate.java
diff --git a/ui/android/java/src/org/chromium/ui/base/ViewAndroidDelegate.java b/ui/android/java/src/org/chromium/ui/base/ViewAndroidDelegate.java
index 82d09ea85aba6095b160d67ec5238c93b1586bb1..41c2e35cfa8b1e03a014aa9007a57d4fdde3aa35 100644
--- a/ui/android/java/src/org/chromium/ui/base/ViewAndroidDelegate.java
+++ b/ui/android/java/src/org/chromium/ui/base/ViewAndroidDelegate.java
@@ -25,6 +25,11 @@ public abstract class ViewAndroidDelegate {
     // TODO(hush): use View#DRAG_FLAG_GLOBAL when Chromium starts to build with API 24.
     private static final int DRAG_FLAG_GLOBAL = 1 << 8;
 
+    private int mPhysicalBackingWidthPix;
+    private int mPhysicalBackingHeightPix;
+
+    private long mNativeViewAndroid;
+
     /**
      * @return An anchor view that can be used to anchor decoration views like Autofill popup.
      */
@@ -104,6 +109,27 @@ public abstract class ViewAndroidDelegate {
                 new View.DragShadowBuilder(imageView), null, DRAG_FLAG_GLOBAL);
     }
 
+    @CalledByNative
+    private void setNativePointer(long nativeViewAndroid) {
+        mNativeViewAndroid = nativeViewAndroid;
+    }
+
+    /**
+     * Called when the underlying surface the compositor draws to changes size.
+     * This may be larger than the viewport size.
+     */
+    public void onPhysicalBackingSizeChanged(int wPix, int hPix) {
+        assert mNativeViewAndroid != 0L;
+
+        if (mPhysicalBackingWidthPix == wPix && mPhysicalBackingHeightPix == hPix) return;
+
+        mPhysicalBackingWidthPix = wPix;
+        mPhysicalBackingHeightPix = hPix;
+
+        nativeOnPhysicalBackingSizeChanged(
+                mNativeViewAndroid, mPhysicalBackingWidthPix, mPhysicalBackingHeightPix);
+    }
+
     /**
      * @return container view that the anchor views are added to. May be null.
      */
@@ -130,4 +156,7 @@ public abstract class ViewAndroidDelegate {
             }
         }.init(containerView);
     }
+
+    private native void nativeOnPhysicalBackingSizeChanged(
+            long nativeViewAndroid, int width, int height);
 }