Add a flag for enabling compositor property trees

cc/base/switches.cc

Index: cc/base/switches.cc
diff --git a/cc/base/switches.cc b/cc/base/switches.cc
index 9a5b03997dc2c1d5dd54596890fc29bf94d144a9..13a9735bff7f42e2b5b8fee170fdc1b0d494eaf7 100644
--- a/cc/base/switches.cc
+++ b/cc/base/switches.cc
@@ -56,6 +56,11 @@ const char kEnableBeginFrameScheduling[] = "enable-begin-frame-scheduling";
 // Enables the GPU benchmarking extension
 const char kEnableGpuBenchmarking[] = "enable-gpu-benchmarking";
 
+// Enables the use of property trees rather than CalcDrawProps for computing
+// draw properties.
+const char kEnableCompositorPropertyTrees[] =
+    "enable-compositor-property-trees";
+
 // Renders a border around compositor layers to help debug and study
 // layer compositing.
 const char kShowCompositedLayerBorders[] = "show-composited-layer-borders";