content: Add switch to enable checker-imaging.

cc/base/switches.cc

Index: cc/base/switches.cc
diff --git a/cc/base/switches.cc b/cc/base/switches.cc
index 55fdf77298689d3fd3328ddf72b27e76533de87e..ca151d2af341ee2fac592e212892abc6875e01a2 100644
--- a/cc/base/switches.cc
+++ b/cc/base/switches.cc
@@ -24,6 +24,9 @@ const char kDisableMainFrameBeforeActivation[] =
 const char kEnableMainFrameBeforeActivation[] =
     "enable-main-frame-before-activation";
 
+// Enables defering image decodes to the image decode service.
+const char kEnableCheckerImaging[] = "enable-checker-imaging";
+
 // Percentage of the browser controls need to be hidden before they will auto
 // hide.
 const char kBrowserControlsHideThreshold[] = "top-controls-hide-threshold";