Add an extension bubble explaining which extensions are in dev mode.

chrome/app/theme/theme_resources.grd

 <?xml version="1.0" encoding="utf-8"?>
 <!-- This grd file contains images that are pre-scaled for device scale
      factors. The image returned by |base::ResourceBundle::GetImageNamed|
      will contain multiple |gfx:ImageSkiaReps| for each scale factors. The
      |fallback_to_low_resolution| attribute controls behavior when
      an image file is missing for target scale factor. If true, chrome
      will automatically scale the 1x image to the target scale factor.
      If false, build will fail due to missing resources. This is
      currently set to true for all resources, but the default will
      become false in near future.
@@ skipping 107 matching lines @@
       <structure type="chrome_scaled_image" name="IDR_BOOKMARK_BAR_APPS_SHORTCUT" file="common/apps_bookmark_bar_icon.png" />
       <if expr="pp_ifdef('chromeos')">
         <structure type="chrome_scaled_image" name="IDR_BUTTON_USER_IMAGE_CHOOSE_FILE" file="choose_file.png" />
         <structure type="chrome_scaled_image" name="IDR_BUTTON_USER_IMAGE_RECORD_VIDEO" file="record_video.png" />
         <structure type="chrome_scaled_image" name="IDR_BUTTON_USER_IMAGE_TAKE_PHOTO" file="take_photo.png" />
       </if>
       <if expr="not pp_ifdef('toolkit_views') and not is_macosx and not is_ios">
         <structure type="chrome_scaled_image" name="IDR_BROWSER_ACTION" file="browser_action.png" />
         <structure type="chrome_scaled_image" name="IDR_BROWSER_ACTION_H" file="browser_action_hover.png" />
         <structure type="chrome_scaled_image" name="IDR_BROWSER_ACTION_P" file="browser_action_pressed.png" />
+        <structure type="chrome_scaled_image" name="IDR_BROWSER_ACTION_HIGHLIGHT" file="browser_action_pressed.png" />
       </if>
       <if expr="pp_ifdef('toolkit_views') or is_macosx or is_ios">
         <structure type="chrome_scaled_image" name="IDR_BROWSER_ACTION" file="common/browser_action_normal.png" />
         <structure type="chrome_scaled_image" name="IDR_BROWSER_ACTION_H" file="common/browser_action_hover.png" />
         <structure type="chrome_scaled_image" name="IDR_BROWSER_ACTION_P" file="common/browser_action_pressed.png" />
+        <structure type="chrome_scaled_image" name="IDR_BROWSER_ACTION_HIGHLIGHT" file="common/browser_action_pressed.png" />
       </if>
       <structure type="chrome_scaled_image" name="IDR_BROWSER_ACTIONS_OVERFLOW" file="common/browser_actions_overflow_normal.png" />
       <structure type="chrome_scaled_image" name="IDR_BROWSER_ACTIONS_OVERFLOW_H" file="common/browser_actions_overflow_hover.png" />
       <structure type="chrome_scaled_image" name="IDR_BROWSER_ACTIONS_OVERFLOW_P" file="common/browser_actions_overflow_pressed.png" />
       <structure type="chrome_scaled_image" name="IDR_CLOSE_BUTTON_MASK" file="close_button_mask.png" />
       <if expr="is_win">
         <structure type="chrome_scaled_image" name="IDR_CONFLICT_FAVICON" file="common/favicon_conflicts.png" />
       </if>
       <!-- Ash doesn't draw rounded content area, so needs a special top
            image. -->
@@ skipping 1016 matching lines @@
       <structure type="chrome_scaled_image" name="IDR_PEOPLE_SEARCH_ACTION_EMAIL" file="common/mail.png" />
       <structure type="chrome_scaled_image" name="IDR_PEOPLE_SEARCH_ACTION_EMAIL_HOVER" file="common/mail_hover.png" />
       <structure type="chrome_scaled_image" name="IDR_PEOPLE_SEARCH_ACTION_EMAIL_PRESSED" file="common/mail_pressed.png" />
       <structure type="chrome_scaled_image" name="IDR_PEOPLE_SEARCH_ACTION_CHAT" file="common/chat.png" />
       <structure type="chrome_scaled_image" name="IDR_PEOPLE_SEARCH_ACTION_CHAT_HOVER" file="common/chat_hover.png" />
       <structure type="chrome_scaled_image" name="IDR_PEOPLE_SEARCH_ACTION_CHAT_PRESSED" file="common/chat_pressed.png" />
 
     </structures>
   </release>
 </grit>