[Picture in Picture] Add strings for confirmation dialog.

These strings will be used for the dialog that appears when the user:
- is closing the tab or window that initiated a Picture-in-Picture
session, or
- is navigating away from a page that initiated a Picture-in-Picture
session.

Dialog implementation is in progress.

Bug: 809982
TBR: grt@chromium.org
Change-Id: I060fb2f21fc93361aeb11f4b605b5012d369e28c
Reviewed-on: https://chromium-review.googlesource.com/1112304
Commit-Queue: apacible <apacible@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569750}

chrome/app/generated_resources.grd

@@ -5663,6 +5663,24 @@ I don't think this site should be blocked!
       <message name="IDS_PICTURE_IN_PICTURE_PLAY_PAUSE_CONTROL_ACCESSIBLE_TEXT" desc="Accessible text label used for the controls button in the Picture-in-Picture window. The button toggles between play and pause controls.">
         Toggle video to play or pause
       </message>
+      <message name="IDS_PICTURE_IN_PICTURE_CONFIRM_CLOSE_TITLE" desc="Text label of the title for the confirmation dialog. This dialog appears when the user tries to close a tab / window while in Picture-in-Picture mode.">
+        Are you sure you want to close this tab?
+      </message>
+      <message name="IDS_PICTURE_IN_PICTURE_CONFIRM_LEAVE_TITLE" desc="Text label of the description for the confirmation dialog. This dialog appears when the user tries to leave a page while in Picture-in-Picture mode.">
+        Are you sure you want to leave this page?
+      </message>
+      <message name="IDS_PICTURE_IN_PICTURE_CONFIRM_DESCRIPTION" desc="Text label of the description for the confirmation dialog. This dialog appears when the user tries to close a tab / window or leave a page while in Picture-in-Picture mode.">
+        The video in Picture-in-Picture will stop playing.
+      </message>
+      <message name="IDS_PICTURE_IN_PICTURE_CONFIRM_CLOSE_TEXT" desc="Text label of the close button. The button appears in the confirmation dialog when the user tries to close a tab or window while in Picture-in-Picture mode.">
+        Close
+      </message>
+      <message name="IDS_PICTURE_IN_PICTURE_CONFIRM_LEAVE_TEXT" desc="Text label of the leave button. The button appears in the confirmation dialog when the user tries to leave a page while in Picture-in-Picture mode.">
+        Leave
+      </message>
+      <message name="IDS_PICTURE_IN_PICTURE_CANCEL_TEXT" desc="Text label of the cancel button. The button appears in the confirmation dialog when the user tries to close a tab / window or leave a page while in Picture-in-Picture mode.">
+        Cancel
+      </message>
 
       <!-- Load State -->
       <message name="IDS_LOAD_STATE_WAITING_FOR_SOCKET_SLOT" desc="Status text when Chrome is at its connection limit, and is waiting for a URL request to complete to free up a connection.">