Allow to have a transparent UA dependent 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 4e2d5d8886d3d14b8093c795c646b63783787e87..2ea5a39f9fbbe67f06701441f72b5c4edcbb54a8 100644
--- a/chrome/browser/ui/views/frame/browser_view.cc
+++ b/chrome/browser/ui/views/frame/browser_view.cc
@@ -2062,8 +2062,13 @@ void BrowserView::InitViews() {
   devtools_web_view_->SetVisible(false);
 
   contents_container_ = new views::View();
-  contents_container_->set_background(views::Background::CreateSolidBackground(
-      GetThemeProvider()->GetColor(ThemeProperties::COLOR_CONTROL_BACKGROUND)));
+
+  if (!base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kNoUADependentBackground))
+    contents_container_->set_background(
+        views::Background::CreateSolidBackground(GetThemeProvider()->GetColor(
+            ThemeProperties::COLOR_CONTROL_BACKGROUND)));
+
   contents_container_->AddChildView(devtools_web_view_);
   contents_container_->AddChildView(contents_web_view_);
   contents_container_->SetLayoutManager(new ContentsLayoutManager(