Make labels of list / thumbnail view button more descriptive.

The button currently says the mode after view change, like "thumbnail
view". It is not clear if it's current mode or the other mode.
This was especially confusing when using screenreaders.

Bug: 755271
Change-Id: Ie305971a32224d6ea715df5ab0fc1e0dd6e2aa91
Reviewed-on: https://chromium-review.googlesource.com/684096Reviewed-by: Naoki Fukino <fukino@chromium.org>
Commit-Queue: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#504335}

chrome/app/chromeos_strings.grdp

@@ -545,10 +545,10 @@ Press any key to continue exploring.
     Cancel selection
   </message>
   <message name="IDS_FILE_BROWSER_CHANGE_TO_LISTVIEW_BUTTON_LABEL" desc="Label for button that changes the view mode to 'list view' mode.">
-    List view
+    Switch to list view
   </message>
   <message name="IDS_FILE_BROWSER_CHANGE_TO_THUMBNAILVIEW_BUTTON_LABEL" desc="Label for button that changes the view mode to 'thumbnail view' mode.">
-    Thumbnail view
+    Switch to thumbnail view
   </message>
   <message name="IDS_FILE_BROWSER_CLOUD_IMPORT_TITLE" desc="Title of the cloud import feature.">
     Cloud backup