Fix accessibility issues in custom tab UI

chrome/android/java/strings/android_chrome_strings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 
 <!-- android_chrome_strings.grd contains strings for Chrome for Android.
 
 FAQ:
   - How do I add, change, or remove a string?
       Just update this file.
   - Translations will happen automatically??
       Yes, indeed. Just add your string before the branch point and
       make the description good.
@@ skipping 1999 matching lines @@
       </message>
       <message name="IDS_ACCESSIBILITY_TOOLBAR_BTN_NEW_INCOGNITO_TAB" desc="Content description for the new incognito tab button.">
         New incognito tab
       </message>
       <message name="IDS_ACCESSIBILITY_TOOLBAR_BTN_TABSWITCHER_TOGGLE" desc="Content description for the button that enters or leaves the tab switcher.">
         <ph name="OPEN_TABS">%1$d<ex>3</ex></ph> open tabs
       </message>
       <message name="IDS_ACCESSIBILITY_TOOLBAR_BTN_HOME" desc="Content description for the home button.">
         Home
       </message>
+      <message name="IDS_ACCESSIBILITY_TOOLBAR_BTN_CLOSE_WEBPAGE" desc="Content description for the button that closes the webpage.">
+        Close webpage

[newt (away), 2015/06/30 18:44:58]

Should this be "Close tab?" We've already got a string for that BTW.

[Yusuf, 2015/06/30 19:52:30]

Yeah, I think that also makes sense in this context. Let's use "Close Tab" and
avoid adding then new string.

[Ian Wen, 2015/06/30 20:14:38]

Done.

+      </message>
       <message name="IDS_ACCESSIBILITY_TOOLBAR_BTN_CUSTOM" desc="Content description for the custom action button.">
         Custom action button
       </message>
       <message name="IDS_ACCESSIBILITY_BTN_REFRESH" desc="Content description for the refresh page button.">
         Refresh page
       </message>
       <message name="IDS_ACCESSIBILITY_BTN_STOP_LOADING" desc="Content description for the stop loading page button.">
         Stop page loading
       </message>
       <message name="IDS_ACCESSIBILITY_FIND_TOOLBAR_BTN_NEXT" desc="Content description for the button to go to the next find in page result.">
@@ skipping 171 matching lines @@
       </message>
       <message name="IDS_HELP_CONTEXT_USAGE_REPORTS" translateable="false">
         send_crash_report
       </message>
       <message name="IDS_HELP_CONTEXT_SAD_TAB" translateable="false">
         mobile_awsnap
       </message>
     </messages>
   </release>
 </grit>