Expose the MacViewsWebUIDialogs feature flag to chrome://flags

chrome/app/generated_resources.grd

Index: chrome/app/generated_resources.grd
diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index 5df0d15047a18e831fca9ca887966c536485238c..7a4a51535ab09f96942a6de788e73cf7c540c60e 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -6584,6 +6584,12 @@ Keep your key file in a safe place. You will need it to create new versions of y
         <message name="IDS_FLAGS_MAC_VIEWS_DIALOGS_DESCRIPTION" desc="Description of the flag to enable toolkit-views browser dialogs on Mac.">
           Causes Chrome on Mac to use a toolkit-views browser dialog when available, in place of the equivalent Cocoa dialog.
         </message>
+        <message name="IDS_FLAGS_MAC_VIEWS_DIALOGS_PHASE2_NAME" desc="Name of the flag to enable the Phase2 set of toolkit-views browser dialogs on Mac." translateable="false">

[msw, 2016/05/24 17:01:29]

nit: Phase numbers don't seem all that meaningful; can we use
'mac-views-[native-]dialogs' and 'mac-views-webui-dialogs' or similar?

[tapted, 2016/05/25 12:01:49]

Done.

+          Toolkit-Views Phase2 Browser Dialogs.
+        </message>
+        <message name="IDS_FLAGS_MAC_VIEWS_DIALOGS_PHASE2_DESCRIPTION" desc="Description of the flag to enable the Phase2 set of toolkit-views browser dialogs on Mac." translateable="false">
+          Use toolkit-views dialogs in place of the native Cocoa dialogs that have square, grey, webui-style buttons.
+        </message>
       </if>
       <if expr="chromeos">
         <message name="IDS_FLAGS_ACCELERATED_MJPEG_DECODE_NAME" desc="Name of the flag to enable accelerated mjpeg decode for captured frame where available.">