Avoid DCHECK when installing a theme with non-opaque NTP bg color.

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

Index: chrome/browser/ui/views/frame/contents_web_view.cc
diff --git a/chrome/browser/ui/views/frame/contents_web_view.cc b/chrome/browser/ui/views/frame/contents_web_view.cc
index fab9246b5a424ba911b62f66af0d71ec09b88176..57f200477772ff0b52508f349b7010fd37e45ba3 100644
--- a/chrome/browser/ui/views/frame/contents_web_view.cc
+++ b/chrome/browser/ui/views/frame/contents_web_view.cc
@@ -58,8 +58,9 @@ void ContentsWebView::OnThemeChanged() {
   // view is sized specially for fullscreen tab capture.  See WebView header
   // file comments for more details.
   const int kBackgroundBrightness = 0x33;  // 20%
-  const SkColor ntp_background =
-      theme->GetColor(ThemeProperties::COLOR_NTP_BACKGROUND);
+  // Make sure the background is opaque.
+  const SkColor ntp_background = color_utils::GetResultingPaintColor(
+      theme->GetColor(ThemeProperties::COLOR_NTP_BACKGROUND), SK_ColorWHITE);
   set_background(views::Background::CreateSolidBackground(
       SkColorGetR(ntp_background) * kBackgroundBrightness / 0xFF,
       SkColorGetG(ntp_background) * kBackgroundBrightness / 0xFF,