Add flag which shows missing 2x resources

ui/base/ui_base_switches.cc

Index: ui/base/ui_base_switches.cc
diff --git a/ui/base/ui_base_switches.cc b/ui/base/ui_base_switches.cc
index b163349fcf6a8f1426a58c2619d1ed9bafc3a389..7d40de89c2950c913e01353ac51f9be4a08432f4 100644
--- a/ui/base/ui_base_switches.cc
+++ b/ui/base/ui_base_switches.cc
@@ -20,6 +20,13 @@ const char kEnableTouchCalibration[] = "enable-touch-calibration";
 // Enable support for touch events.
 const char kEnableTouchEvents[] = "enable-touch-events";
 
+// Generates a 2x version of resources for which no 2x version is available or
+// the 2x version is of an incorrect size and applies a red mask to the
+// resource. Resources for which hidpi is not supported because of software
+// reasons will show up pixelated.
+const char kHighlightMissing2xResources[] =
+    "highlight-missing-2x-resources";
+
 // The language file that we want to try to open. Of the form
 // language[-country] where language is the 2 letter code from ISO-639.
 const char kLang[] = "lang";