Add onBackgroundColorChanged to Tab and TabObserver

chrome/android/java/src/org/chromium/chrome/browser/EmptyTabObserver.java

Index: chrome/android/java/src/org/chromium/chrome/browser/EmptyTabObserver.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/EmptyTabObserver.java b/chrome/android/java/src/org/chromium/chrome/browser/EmptyTabObserver.java
index 9a5b09f9628b7e4a15f7c6a8be3f1594bf89cc55..b690c577d4a81b72d56d3f66e6b6f6b6e6fe0b1f 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/EmptyTabObserver.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/EmptyTabObserver.java
@@ -83,6 +83,9 @@ public class EmptyTabObserver implements TabObserver {
     public void onDidDetachInterstitialPage(Tab tab) { }
 
     @Override
+    public void onBackgroundColorChanged(Tab tab, int color) { }
+
+    @Override
     public void webContentsCreated(Tab tab, long sourceWebContents, long openerRenderFrameId,
             String frameName, String targetUrl, long newWebContents) { }
 }