[Enhanced Bookmark] Change "Bookmark Bar" to "Bookmark bar" on Android

Upper case letters for all words is not Android style.

BUG=NONE

Review URL: https://codereview.chromium.org/1029423011

Cr-Commit-Position: refs/heads/master@{#322603}

components/bookmark_bar_strings.grdp

@@ -15,7 +15,7 @@
       Desktop bookmarks
     </message>
     <message name="IDS_ENHANCED_BOOKMARK_BAR_FOLDER_NAME" desc="Mobile: Name shown in the tree for the desktop bookmarks folder when enhanced bookmark is enabled.">
-      Bookmarks Bar
+      Bookmarks bar
     </message>
   </if>
   <if expr="is_ios">