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 48e37a65e0e72bcdd39ce1ee47f1ce6b2f09c9c8..25de1569488bd6663e8981ade95bcb1af06ba1c6 100644
--- a/cc/base/switches.cc
+++ b/cc/base/switches.cc
@@ -35,6 +35,11 @@ const char kEnableRightAlignedScheduling[] = "enable-right-aligned-scheduling";
 const char kEnableTopControlsPositionCalculation[] =
     "enable-top-controls-position-calculation";
 
+// For any layers that can get drawn directly to screen, draw them with the Skia
+// GPU backend.  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";