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..8bb45951dee4fa5aaf02bb83eff5bb780bf6bb62 100644
--- a/ui/base/ui_base_switches.cc
+++ b/ui/base/ui_base_switches.cc
@@ -28,6 +28,13 @@ const char kLang[] = "lang";
 // mix of 1x and 2x and loading them may break the UI on 2x display.
 const char kLoad2xResources[] = "load-2x-resources";
 
+// 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";
+
 // Load the locale resources from the given path. When running on Mac/Unix the
 // path should point to a locale.pak file.
 const char kLocalePak[] = "locale_pak";