Add flag for drawing layers to screen with Ganesh

cc/base/switches.cc

Index: cc/base/switches.cc
diff --git a/cc/base/switches.cc b/cc/base/switches.cc
index a90dc6728fb1dd83199d15392db62299caaeae9e..2ef95d91a9dee46244330529aa3b8aea7a8ed75b 100644
--- a/cc/base/switches.cc
+++ b/cc/base/switches.cc
@@ -38,6 +38,10 @@ const char kEnableTopControlsPositionCalculation[] =
 // Enable solid tile color and transparent tile metrics.
 const char kEnablePredictionBenchmarking[] = "enable-prediction-benchmarking";
 
+// For any layers that can get drawn directly to screen, draw them with Ganesh.
+// Only valid with gl rendering + threaded compositing + impl-side painting.
+const char kForceDirectLayerDrawing[] = "force-direct-layer-drawing";
+
 // The height of the movable top controls.
 const char kTopControlsHeight[] = "top-controls-height";