cc: Add a blocksPendingCommit flag to LayerImpl

cc/texture_layer.cc

Index: cc/texture_layer.cc
diff --git a/cc/texture_layer.cc b/cc/texture_layer.cc
index 2cb8ad7406ec46f8c1ef7bd58c9a2116e956674d..a00feeb094f1116465d272e8d39179e88853b10b 100644
--- a/cc/texture_layer.cc
+++ b/cc/texture_layer.cc
@@ -131,4 +131,12 @@ void TextureLayer::pushPropertiesTo(LayerImpl* layer)
     m_contentCommitted = drawsContent();
 }
 
+bool TextureLayer::blocksPendingCommit() const
+{
+    // Double-buffered texture layers need to be blocked until they can be made
+    // triple-buffered.  Single-buffered layers already prevent draws, so
+    // can block too for simplicity.
+    return true;
+}
+
 }  // namespace cc