Add switch (for cast_shell) to defer creation of GPU process.

content/public/common/content_switches.cc

Index: content/public/common/content_switches.cc
diff --git a/content/public/common/content_switches.cc b/content/public/common/content_switches.cc
index 69d0941ea98aa3d3b59d69990e50d468da97f344..602552f2a22a3de83f31fb4183cfdac2b373a4b1 100644
--- a/content/public/common/content_switches.cc
+++ b/content/public/common/content_switches.cc
@@ -64,6 +64,11 @@ const char kDebugPluginLoading[] = "debug-plugin-loading";
 const char kDefaultTileWidth[]              = "default-tile-width";
 const char kDefaultTileHeight[]             = "default-tile-height";
 
+// Defer GPU process creation.  Disables default logic for starting GPU process
+// during browser main thread initialization.  Content embedder is responsible
+// for creating GPU process before it's needed.
+const char kDeferGpuProcessCreation[]       = "defer-gpu-process-creation";
+
 // Disable antialiasing on 2d canvas.
 const char kDisable2dCanvasAntialiasing[]   = "disable-canvas-aa";