Allow to have a transparent UA dependent background.

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

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/views/frame/browser_view.h"
 
 #include <stdint.h>
 #include <algorithm>
 #include <utility>
 
@@ skipping 2110 matching lines @@
   contents_web_view_->SetEmbedFullscreenWidgetMode(true);
 
   web_contents_close_handler_.reset(
       new WebContentsCloseHandler(contents_web_view_));
 
   devtools_web_view_ = new views::WebView(browser_->profile());
   devtools_web_view_->set_id(VIEW_ID_DEV_TOOLS_DOCKED);
   devtools_web_view_->SetVisible(false);
 
   contents_container_ = new views::View();
+  // FIXME: Clear alpha only upon a call to
+  // content::RenderWidgetHostView->SetBackgroundColor(SK_ColorTRANSPARENT).
   contents_container_->set_background(views::Background::CreateSolidBackground(
-      GetThemeProvider()->GetColor(ThemeProperties::COLOR_CONTROL_BACKGROUND)));
+      GetThemeProvider()->GetColor(ThemeProperties::COLOR_CONTROL_BACKGROUND) &
+      0x00FFFFFF));

[trchen, 2016/02/25 02:30:12]

What does this mean? Is it pre-multiplied alpha or not?
If pre-multiplied, masking alpha to 0 will result in invalid color.
If not pre-multiplied, masking alpha to 0 is equivalent to fully transparent.
Either way this looks weird and deserves a comment.

[Julien Isorce Samsung, 2016/02/25 11:33:55]

Sorry for the confusion, this code has no intention to be merged. In the first
comment of this CL I refer to that as "demo" code. I just force the theme to
have its background fully transparent.
In real world, the hypothetic custom theme would defines its background as fully
transparent.

+
   contents_container_->AddChildView(devtools_web_view_);
   contents_container_->AddChildView(contents_web_view_);
   contents_container_->SetLayoutManager(new ContentsLayoutManager(
       devtools_web_view_, contents_web_view_));
   AddChildView(contents_container_);
   set_contents_view(contents_container_);
 
   // Top container holds tab strip and toolbar and lives at the front of the
   // view hierarchy.
   top_container_ = new TopContainerView(this);
@@ skipping 588 matching lines @@
 }
 
 extensions::ActiveTabPermissionGranter*
 BrowserView::GetActiveTabPermissionGranter() {
   content::WebContents* web_contents = GetActiveWebContents();
   if (!web_contents)
     return nullptr;
   return extensions::TabHelper::FromWebContents(web_contents)
       ->active_tab_permission_granter();
 }