[Android] Make keyboard accessory sheet front-most item

Before this CL, elements like Duet's bottom toolbar are drawn over the
keyboard accessory sheet.

Therefore (just as the accessory bar), move the accessory sheet to the
front before showing it. That ensures that elements that don't treat
the sheet as a keyboard (yet) are overlaid and hidden.
The accessory isn't click-through and reduces the content area which
effectively hides all elements below it as if they weren't there.

Bug: 880253
Change-Id: I7fb201c6dcc9e15c3c31df8e0b9650225826873a
Reviewed-on: https://chromium-review.googlesource.com/1209282Reviewed-by: Ioana Pandele <ioanap@chromium.org>
Commit-Queue: Friedrich Horschig [CEST] <fhorschig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589129}

chrome/android/java/src/org/chromium/chrome/browser/autofill/keyboard_accessory/AccessorySheetViewBinder.java

@@ -21,6 +21,7 @@ class AccessorySheetViewBinder {
             viewPager.setAdapter(
                     AccessorySheetCoordinator.createTabViewAdapter(model.getTabList(), viewPager));
         } else if (propertyKey == PropertyKey.VISIBLE) {
+            viewPager.bringToFront(); // Ensure toolbars and other containers are overlaid.
             viewPager.setVisibility(model.isVisible() ? View.VISIBLE : View.GONE);
         } else if (propertyKey == PropertyKey.HEIGHT) {
             ViewGroup.LayoutParams p = viewPager.getLayoutParams();