Add flag to disable impl-side painting

cc/switches.cc

Index: cc/switches.cc
diff --git a/cc/switches.cc b/cc/switches.cc
index ec74e8394838ed3652b4fa8c4e57244548217096..efd0dbe1dd3dffaf5b729403b059ef839ec47ffd 100644
--- a/cc/switches.cc
+++ b/cc/switches.cc
@@ -17,6 +17,9 @@ const char kDisableThreadedAnimation[]      = "disable-threaded-animation";
 // Send a message for every frame from the impl thread to the parent compositor.
 const char kEnableCompositorFrameMessage[] = "enable-compositor-frame-message";
 
+// Paint content on the main thread instead of the compositor thread.
+const char kDisableImplSidePainting[] = "disable-impl-side-painting";
+
 // Paint content on the compositor thread instead of the main thread.
 const char kEnableImplSidePainting[] = "enable-impl-side-painting";