Implement on demand quad rasterization for PicturePiles.

cc/test/layer_tree_test_common.cc

Index: cc/test/layer_tree_test_common.cc
diff --git a/cc/test/layer_tree_test_common.cc b/cc/test/layer_tree_test_common.cc
index e9be315ff0d790709fe6ecfbe2af67aacb63e4c6..d73367007b494a11458e670888c8a98449370a55 100644
--- a/cc/test/layer_tree_test_common.cc
+++ b/cc/test/layer_tree_test_common.cc
@@ -316,10 +316,13 @@ void ThreadedTest::endTest()
 {
     // For the case where we endTest during beginTest(), set a flag to indicate that
     // the test should end the second beginTest regains control.
-    if (m_beginning)
+    if (m_beginning) {
         m_endWhenBeginReturns = true;
-    else
-        proxy()->MainThread()->PostTask(base::Bind(&ThreadedTest::realEndTest, m_mainThreadWeakPtr));
+    } else {
+        // Racy timeouts and explicit endTest calls might have cleaned up the tree host.
+        if (proxy())

[Leandro Graciá Gil, 2013/03/19 17:30:58]

Found flakiness here when creating the new layer-based pixel test. This should
fix it.

+            proxy()->MainThread()->PostTask(base::Bind(&ThreadedTest::realEndTest, m_mainThreadWeakPtr));
+    }
 }
 
 void ThreadedTest::endTestAfterDelay(int delayMilliseconds)