Introduce ViewRoot to forward 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
new file mode 100644
index 0000000000000000000000000000000000000000..c224e8e3ed8c9cdfd31b3ed2e783e090ea42a4e7
--- /dev/null
+++ b/ui/android/java/src/org/chromium/ui/base/ViewRoot.java
@@ -0,0 +1,50 @@
+// 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.
+
+package org.chromium.ui.base;
+
+import org.chromium.base.annotations.CalledByNative;
+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 {
+    // The corresponding native ViewAndroid. This object can only be used while
+    // the native instance is alive.
+    private long mNativeView;
+
+    @CalledByNative
+    private static ViewRoot create(long nativeView) {
+        return new ViewRoot(nativeView);
+    }
+
+    private ViewRoot(long nativeView) {
+        mNativeView = nativeView;
+    }
+
+    /**
+     * Called when the underlying surface the compositor draws to changes size.
+     * This may be larger than the viewport size.
+     * @param width Width of the physical backing surface.
+     * @param height Height of the physical backing surface.
+     */
+    public void onPhysicalBackingSizeChanged(int width, int height) {
+        assert mNativeView != 0;
+        nativeOnPhysicalBackingSizeChanged(mNativeView, width, height);
+    }
+
+    @CalledByNative
+    private void onDestroyNativeView() {
+        mNativeView = 0;
+    }
+
+    private static native void nativeOnPhysicalBackingSizeChanged(long viewAndroid,
+            int width, int height);
+}