Upstream oodles of Chrome for Android code into Chromium.

chrome/android/java_staging/src/org/chromium/chrome/browser/compositor/layouts/SceneChangeObserver.java

Index: chrome/android/java_staging/src/org/chromium/chrome/browser/compositor/layouts/SceneChangeObserver.java
diff --git a/chrome/android/java_staging/src/org/chromium/chrome/browser/compositor/layouts/SceneChangeObserver.java b/chrome/android/java_staging/src/org/chromium/chrome/browser/compositor/layouts/SceneChangeObserver.java
new file mode 100644
index 0000000000000000000000000000000000000000..74bc4eddaae8d66354befa14c3da2f33491a6765
--- /dev/null
+++ b/chrome/android/java_staging/src/org/chromium/chrome/browser/compositor/layouts/SceneChangeObserver.java
@@ -0,0 +1,23 @@
+// 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.layouts;
+
+/**
+ * An observer that listens for active {@link Layout} changes.
+ */
+public interface SceneChangeObserver {
+    /**
+     * Called when a layout wants to hint that a new tab might be selected soon.  This is not called
+     * every time a tab is selected.
+     * @param tabId The id of the tab that might be selected soon.
+     */
+    void onTabSelectionHinted(int tabId);
+
+    /**
+     * Called when the active {@link Layout} changes.
+     * @param layout The new active {@link Layout}.
+     */
+    void onSceneChange(Layout layout);
+}