Media Controls a11y: add text/description/role to more controls components.

content/app/strings/content_strings.grd

Index: content/app/strings/content_strings.grd
diff --git a/content/app/strings/content_strings.grd b/content/app/strings/content_strings.grd
index c72fd5e424e7731c3a083abf61cd9b5de0db52d6..1e53efbf09501de70b69335063d73b6ce051b4b6 100644
--- a/content/app/strings/content_strings.grd
+++ b/content/app/strings/content_strings.grd
@@ -620,6 +620,14 @@ below:
         control remote playback
       </message>
 
+      <message name="IDS_AX_MEDIA_DOWNLOAD_BUTTON" desc="Media controls download button.">
+        download file

[dmazzoni, 2016/10/10 03:39:52]

Maybe download media?

[mlamouri (slow - plz ping), 2016/10/10 04:27:13]

Done. I'm not entirely sure people really understand "download media" compared
to "download file" but I'm no native speaker so :)

+      </message>
+
+      <message name="IDS_AX_MEDIA_OVERFLOW_BUTTON" desc="Media controls overflow button.">
+        show more controls

[dmazzoni, 2016/10/10 03:39:52]

How about "more media controls"?

Saying "Show more" implies it just toggles showing more, but really this is just
a menu button

[mlamouri (slow - plz ping), 2016/10/10 04:27:13]

Done.

+      </message>
+
       <message name="IDS_AX_MEDIA_AUDIO_ELEMENT_HELP" desc="Accessible help of audio controls">
         audio
       </message>
@@ -692,6 +700,14 @@ below:
         control remote playback
       </message>
 
+      <message name="IDS_AX_MEDIA_DOWNLOAD_BUTTON_HELP" desc="accessibility help description for download button.">
+        download file

[dmazzoni, 2016/10/10 03:39:52]

This isn't necessary if the text is identical to the button title. The purpose
of the help string is if the button title is short and concise and a longer
description might help clarify what happens when you click on it. In this case I
think just skipping it is better.

[mlamouri (slow - plz ping), 2016/10/10 04:27:13]

Done. FTR, a lot of "help" description seems to be exactly like the alt text.

+      </message>
+
+      <message name="IDS_AX_MEDIA_OVERFLOW_BUTTON_HELP" desc="accessibility help description for overflow button.">
+        more options
+      </message>
+
       <message name="IDS_AX_MILLISECOND_FIELD_TEXT" desc="Accessible description of the millisecond field in a date/time control">
         Milliseconds
       </message>
@@ -852,9 +868,6 @@ below:
         Please lengthen this text to <ph name="MIN_CHARACTERS">$2<ex>101</ex></ph> characters or more (you are currently using <ph name="CURRENT_LENGTH">$1<ex>100</ex></ph> characters).
       </message>
 
-      <message name="IDS_AX_MEDIA_OVERFLOW_BUTTON" desc="Media controls overflow menu.">
-        Overflow menu
-      </message>
       <message name="IDS_MEDIA_OVERFLOW_MENU_CLOSED_CAPTIONS" desc="Media controls overflow menu item label for a closed captions button. The text for this overflow menu should be short.">
         Captions
       </message>