Chromecast: use ARGB format for WebColor.

R=lcwu@chromium.org
BUG=None

Review URL: https://codereview.chromium.org/615113002

Cr-Commit-Position: refs/heads/master@{#297458}

chromecast/shell/renderer/cast_content_renderer_client.cc

@@ -21,8 +21,9 @@ namespace shell {
 
 namespace {
 
-// Default background color to set for WebViews
-const blink::WebColor kColorBlack = 0x000000FF;
+// Default background color to set for WebViews. WebColor is in ARGB format
+// though the comment of WebColor says it is in RGBA.
+const blink::WebColor kColorBlack = 0xFF000000;
 
 }  // namespace