Make sure to fill canvas opaquely when painting bookmark bar background.

chrome/browser/ui/views/frame/browser_view.cc

Index: chrome/browser/ui/views/frame/browser_view.cc
diff --git a/chrome/browser/ui/views/frame/browser_view.cc b/chrome/browser/ui/views/frame/browser_view.cc
index bfb23b6c32151a007111121d3ec31ebea3c7dc66..95396a77337c9f9afa89fecaf8238f86880e33ee 100644
--- a/chrome/browser/ui/views/frame/browser_view.cc
+++ b/chrome/browser/ui/views/frame/browser_view.cc
@@ -223,17 +223,16 @@ void PaintHorizontalBorder(gfx::Canvas* canvas,
 // content page in the very near future, at which time, these local functions
 // will be removed.
 void PaintDetachedBookmarkBar(gfx::Canvas* canvas,
-                              BookmarkBarView* view,
-                              Profile* profile) {
+                              BookmarkBarView* view) {
   // Paint background for detached state; if animating, this is fade in/out.
-  const ui::ThemeProvider& tp =
-      ThemeService::GetThemeProviderForProfile(profile);
+  const ui::ThemeProvider* tp = view->GetThemeProvider();
   canvas->DrawColor(
-      tp.GetColor(ThemeProperties::COLOR_DETACHED_BOOKMARK_BAR_BACKGROUND));
+      tp->GetColor(ThemeProperties::COLOR_DETACHED_BOOKMARK_BAR_BACKGROUND));
+
   // Draw the separators above and below bookmark bar;
   // if animating, these are fading in/out.
   SkColor separator_color =
-      tp.GetColor(ThemeProperties::COLOR_DETACHED_BOOKMARK_BAR_SEPARATOR);
+      tp->GetColor(ThemeProperties::COLOR_DETACHED_BOOKMARK_BAR_SEPARATOR);
 
   if (ui::MaterialDesignController::IsModeMaterial()) {
     BrowserView::Paint1pxHorizontalLine(
@@ -262,8 +261,7 @@ void PaintBackgroundAttachedMode(gfx::Canvas* canvas,
                                  const ui::ThemeProvider* theme_provider,
                                  const gfx::Rect& bounds,
                                  const gfx::Point& background_origin) {
-  canvas->FillRect(bounds,
-                   theme_provider->GetColor(ThemeProperties::COLOR_TOOLBAR));
+  canvas->DrawColor(theme_provider->GetColor(ThemeProperties::COLOR_TOOLBAR));
 
   // Always tile the background image in pre-MD. In MD, only tile if there's a
   // non-default image.
@@ -424,6 +422,10 @@ BookmarkBarViewBackground::BookmarkBarViewBackground(
 
 void BookmarkBarViewBackground::Paint(gfx::Canvas* canvas,
                                       views::View* view) const {
+  // Start with a blank canvas --- the attached and detached colors may not be
+  // fully opaque.
+  canvas->DrawColor(SK_ColorWHITE);

[sky, 2016/04/05 19:14:01]

Why is white the right color here?

[Evan Stade, 2016/04/05 19:36:10]

That is a good question. Initially I used black, but I found that white
preserved pre-MD behavior. I didn't investigate thoroughly why this was
(presumably before an opaque layer was added, we were painting white at some
higher level in the view hierarchy).

[Evan Stade, 2016/04/05 20:31:51]

I looked into it and I think that previously the frame was providing the base
color, so I've updated accordingly.

+
   int toolbar_overlap = bookmark_bar_view_->GetToolbarOverlap();
 
   SkAlpha detached_alpha = static_cast<SkAlpha>(
@@ -439,7 +441,7 @@ void BookmarkBarViewBackground::Paint(gfx::Canvas* canvas,
   // While animating, set opacity to cross-fade between attached and detached
   // backgrounds including their respective separators.
   canvas->SaveLayerAlpha(detached_alpha);
-  PaintDetachedBookmarkBar(canvas, bookmark_bar_view_, browser_->profile());
+  PaintDetachedBookmarkBar(canvas, bookmark_bar_view_);
   canvas->Restore();
 }