[Android] Upstream scene layers

chrome/android/java/src/org/chromium/chrome/browser/compositor/scene_layer/SceneOverlayLayer.java

Index: chrome/android/java/src/org/chromium/chrome/browser/compositor/scene_layer/SceneOverlayLayer.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/compositor/scene_layer/SceneOverlayLayer.java b/chrome/android/java/src/org/chromium/chrome/browser/compositor/scene_layer/SceneOverlayLayer.java
new file mode 100644
index 0000000000000000000000000000000000000000..9cf31cdc602c2bd774739c338990c354bba9fb95
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/compositor/scene_layer/SceneOverlayLayer.java
@@ -0,0 +1,17 @@
+// Copyright 2015 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.chrome.browser.compositor.scene_layer;
+
+/**
+ * An extension of SceneLayer for SceneOverlay.
+ */
+public abstract class SceneOverlayLayer extends SceneLayer {
+    /**
+     * Sets a content tree inside this scene overlay tree.
+     * TODO(jaekyun): We need to rename this method later because the meaning of "content" isn't
+     * clear.
+     */
+    public abstract void setContentTree(SceneLayer contentTree);
+}