Add seek forward/backward controls in MediaNotification

chrome/android/java/strings/android_chrome_strings.grd

Index: chrome/android/java/strings/android_chrome_strings.grd
diff --git a/chrome/android/java/strings/android_chrome_strings.grd b/chrome/android/java/strings/android_chrome_strings.grd
index c602646fa9482813c12738680832eb603c4561f3..0b40a8755ee5f006a222673f5d679ca264491133 100644
--- a/chrome/android/java/strings/android_chrome_strings.grd
+++ b/chrome/android/java/strings/android_chrome_strings.grd
@@ -1896,6 +1896,12 @@ To obtain new licenses, connect to the internet and play your downloaded content
       <message name="IDS_ACCESSIBILITY_NEXT_TRACK" desc="Content description for the next track button that switches media to the next track.">
         Next track
       </message>
+      <message name="IDS_ACCESSIBILITY_SEEK_FORWARD" desc="Content description for the seek forward button that seeks media to a later position.">

[gone, 2016/11/28 19:23:21]

Don't need to say "content description".  This is for human translators to read
and figure out what they're trying to translate, not for developers trying to
figure out where this thing goes.

[Zhiqiang Zhang (Slow), 2016/11/29 16:45:40]

Removed all "content description".

+        Seek forward
+      </message>
+      <message name="IDS_ACCESSIBILITY_SEEK_BACKWARD" desc="Content description for the seek backward button that seeks media to an earlier position.">
+        Seek backward
+      </message>
 
       <!-- New Tab Page strings -->
       <message name="IDS_NTP_BOOKMARKS" desc="Text for bookmarks button [CHAR-LIMIT=20]">