Draw background opaquely on MD download items.

chrome/browser/ui/views/download/download_item_view_md.cc

Index: chrome/browser/ui/views/download/download_item_view_md.cc
diff --git a/chrome/browser/ui/views/download/download_item_view_md.cc b/chrome/browser/ui/views/download/download_item_view_md.cc
index 0d3082de0ae6d8e3c1c400175e42f5e4dee01cf8..6fcd44a45d3d220c3d4b97d428826c82e10797d1 100644
--- a/chrome/browser/ui/views/download/download_item_view_md.cc
+++ b/chrome/browser/ui/views/download/download_item_view_md.cc
@@ -462,6 +462,7 @@ void DownloadItemViewMd::GetAccessibleState(ui::AXViewState* state) {
 
 void DownloadItemViewMd::OnThemeChanged() {
   UpdateColorsFromTheme();
+  SchedulePaint();
 }
 
 void DownloadItemViewMd::AddInkDropLayer(ui::Layer* ink_drop_layer) {
@@ -588,6 +589,12 @@ void DownloadItemViewMd::AnimationProgressed(const gfx::Animation* animation) {
 }
 
 void DownloadItemViewMd::OnPaint(gfx::Canvas* canvas) {
+  // Make sure to draw |this| opaquely. Since the toolbar color can be partially
+  // transparent, start with an opaque black backdrop.
+  canvas->DrawColor(SK_ColorBLACK);

[sky, 2016/04/05 20:26:55]

Why is black the right color here? Sorry for a similar question as the last, the
choice of color seems arbitrary and I'm trying to understand why we go with
black here vs white in the bookmarkbar vs anything?

Actually, more generally why is it important to paint any color? If the theme
wants a transparent color shouldn't that be ok? By which I mean ultimately some
ancestor of the downloaditem should paint a color, right?

[Evan Stade, 2016/04/05 20:46:54]

Black seems more right to me than white because an opaque canvas starts off as
black as I understand it. The layer that we add for the ink drop hosting gives
us a non-opaque canvas, so we have to paint opaquely in order to draw text on
top of it correctly.
From the theme author's perspective, what do you think a transparent color
should mean? What is it painted on top of? Honestly it would make more sense to
me not to support transparency at all, but apparently we've handled it
gracefully in the past. I suspect this changed because the canvas we're getting
is no longer created as opaque: 

https://code.google.com/p/chromium/codesearch#chromium/src/ui/gfx/canvas.cc&l=37
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/skia/i...

+  canvas->DrawColor(
+      GetThemeProvider()->GetColor(ThemeProperties::COLOR_TOOLBAR));
+
   DrawStatusText(canvas);
   DrawFilename(canvas);
   DrawIcon(canvas);