[NTP] Add strings for button labels for a11y

Bug: 858885
Change-Id: I9ea772268411272c86e333ec4041b3e17b38f3af
Reviewed-on: https://chromium-review.googlesource.com/1142541
Commit-Queue: Kyle Milka <kmilka@chromium.org>
Reviewed-by: Mathieu Perreault <mathp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577188}

chrome/app/generated_resources.grd

@@ -4783,6 +4783,15 @@ Keep your key file in a safe place. You will need it to create new versions of y
       <message name="IDS_NTP_CUSTOM_BG_IMAGE_NOT_USABLE" desc="Error message for when an uploaded image is not usuable as a custom background. (On the New Tab Page)">
         This image can't be used. Choose a different image.
       </message>
+      <message name="IDS_NTP_CUSTOM_BG_BACK_LABEL" desc="Accessibility label for the back arrow on the background picker dialog. (On the New Tab Page)">
+        Back
+      </message>
+      <message name="IDS_NTP_CUSTOM_BG_CUSTOMIZE_NTP_LABEL" desc="Accessibility label for the gear icon. (On the New Tab Page)">
+        Customize this page
+      </message>
+      <message name="IDS_NTP_CUSTOM_BG_GOOGLE_PHOTO_LABEL" desc="Accessibility label for a Google Photos image tile. (On the New Tab Page)">
+        Photo
+      </message>
 
       <!--Tooltip strings-->
       <message name="IDS_TOOLTIP_BACK" desc="The tooltip for back button">

chrome/app/generated_resources_grd/IDS_NTP_CUSTOM_BG_BACK_LABEL.png.sha1

+f29b09ad3bbe74cf10e3e7a7becf2a4a1aefae41
\ No newline at end of file

chrome/app/generated_resources_grd/IDS_NTP_CUSTOM_BG_CUSTOMIZE_NTP_LABEL.png.sha1

+28d6b42dde96828b2f8adb23a8846787a6ed7fa7
\ No newline at end of file

chrome/app/generated_resources_grd/IDS_NTP_CUSTOM_BG_GOOGLE_PHOTO_LABEL.png.sha1

+b3ce3cdb8cdfbe65b6cd2d5a25ae93b2f3eeff3b
\ No newline at end of file