Increase Duet menu distance from bottom

This patch is attempting to fix an issue that is causing the overflow
menu to appear offscreen on certain HTC devices on Android N by
increasing the margin between the bottom of the menu and the bottom
of the screen. The thought is that the menu is originally positioned
slightly offscreen and Android tries to reposition the menu; on some
devices this is broken and positions the menu so it is mostly
invisible.

Bug: 894555
Change-Id: Idbb0b4b96e20586a4e15a876f485208504ce72c4
Reviewed-on: https://chromium-review.googlesource.com/c/1278289Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599227}

chrome/android/java/res/values/dimens.xml

@@ -57,7 +57,7 @@
          via scrolling. -->
     <dimen name="menu_vertical_fade_distance">15dp</dimen>
     <dimen name="menu_badge_translation_y_distance">6dp</dimen>
-    <dimen name="menu_negative_vertical_offset_not_top_anchored">4dp</dimen>
+    <dimen name="menu_negative_vertical_offset_not_top_anchored">8dp</dimen>
 
     <!-- Menu button dragging related dimensions -->
     <dimen name="auto_scroll_full_velocity">500dp</dimen>