Reduce overdraw on bookmark bar

chrome/browser/ui/views/bookmarks/bookmark_bar_view.cc

Index: chrome/browser/ui/views/bookmarks/bookmark_bar_view.cc
diff --git a/chrome/browser/ui/views/bookmarks/bookmark_bar_view.cc b/chrome/browser/ui/views/bookmarks/bookmark_bar_view.cc
index ce37e63e3dbf78cae113307a1998cf5fb894aa80..8fd10480ee79058275fb7282c5a76fd2f332c7e7 100644
--- a/chrome/browser/ui/views/bookmarks/bookmark_bar_view.cc
+++ b/chrome/browser/ui/views/bookmarks/bookmark_bar_view.cc
@@ -605,7 +605,7 @@ BookmarkBarView::BookmarkBarView(Browser* browser, BrowserView* browser_view)
   // Don't let the bookmarks show on top of the location bar while animating.
   SetPaintToLayer();
   layer()->SetMasksToBounds(true);
-  layer()->SetFillsBoundsOpaquely(false);
+  layer()->SetFillsBoundsOpaquely(true);

[sky, 2017/05/26 13:40:53]

I'm surprised this would work. Don't we need the the bookmark bar to show
through in some cases? Same themes or animations or on the ntp when detached?

[yiyix, 2017/05/26 18:30:33]

I believe that it's opaque for both attached and detached bookmark bars. 
For themes:
For attached case, we first paint background color of the toolbar, then we paint
the image from the theme for the bookmark bar. (as shown in
https://cs.chromium.org/chromium/src/chrome/browser/ui/views/frame/browser_vi...
). I believe the background of the toolbar is always opaque. I found this bug,
which requests it to be transparent and marked as "won't fix",
https://bugs.chromium.org/p/chromium/issues/detail?id=244892. I also tried to
search transparent theme in the app store and could not find any. So I was
convinced it's safe to mark the layer as opaque.

For detached case, I found this comment, which explains the color for view must
be painted opaquely and the layer can be semi-transparent, so it's safe to make
the bookmark bar layer as opaque as well.
https://cs.chromium.org/chromium/src/chrome/browser/ui/views/frame/browser_vi...

 
   size_animation_.Reset(1);
 }