Add high contrast keyboard shortcut to keyboard overlay

chrome/app/chromeos_strings.grdp

Index: chrome/app/chromeos_strings.grdp
diff --git a/chrome/app/chromeos_strings.grdp b/chrome/app/chromeos_strings.grdp
index f60ad8757ef5608c7293ec8cc6dbba5def3db48e..83f8d5e65d214234c7684e4f489df4ea6c88ae95 100644
--- a/chrome/app/chromeos_strings.grdp
+++ b/chrome/app/chromeos_strings.grdp
@@ -4849,6 +4849,9 @@ Battery full
   <message name="IDS_KEYBOARD_OVERLAY_TOGGLE_CHROMEVOX_SPOKEN_FEEDBACK" desc="The text in the keyboard overlay to explain the shortcut (enable or disable spoken feedback).">
     ChromeVox (spoken feedback)
   </message>
+  <message name="IDS_KEYBOARD_OVERLAY_TOGGLE_HIGH_CONTRAST_MODE" desc="The text in the keyboard overlay to explain the shortcut (Toggle high contrast mode).">
+    Toggle High Contrast Mode

[stevenjb, 2017/02/16 19:45:13]

Please double check this with UX (I would expect just 'High contrast mode')

[afakhry, 2017/02/16 21:07:44]

This is how dmazzoni wrote it when the shortcut used to be Ctrl+Alt+H, but that
was reverted 5 months ago.

+  </message>
   <message name="IDS_KEYBOARD_OVERLAY_TOGGLE_PROJECTION_TOUCH_HUD" desc="The text in the keyboard overlay to explain the shortcut.">
     Projection touch HUD
   </message>