Add a command-line switch --enable-per-tile-painting.

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 c074ff9a8aeb3964ebc17e1f6596db386cfd4bae..f9564165bc86cf889d49cab471230ceef75488db 100644
--- a/content/public/common/content_switches.cc
+++ b/content/public/common/content_switches.cc
@@ -555,4 +555,10 @@ const char kUseSystemSSL[]                  = "use-system-ssl";
 const char kRendererCheckFalseTest[]        = "renderer-check-false-test";
 #endif
 
+// Enable per-tile page drawing.
+// Please note that this flag is honored only if chromium is compiled with
+// SKIA_GPU flag, which can be enabled by setting use_skia_gpu variable to 1
+// in build/features_override.gypi.
+const char kEnablePerTileDrawing[]          = "enable-per-tile-drawing";
+
 }  // namespace switches