Propagate theme color updates to the WebContentsDelegates.

When the theme color on a page changes after the first visually non-
empty paint, this should be propagated to the delegates so that the
browser UI can be updated accordingly.

BUG=474371

Review URL: https://codereview.chromium.org/1149073006

Cr-Commit-Position: refs/heads/master@{#332180}
diff --git a/content/browser/web_contents/web_contents_impl.h b/content/browser/web_contents/web_contents_impl.h
index 51efdb4..a6c62111 100644
--- a/content/browser/web_contents/web_contents_impl.h
+++ b/content/browser/web_contents/web_contents_impl.h
@@ -1112,6 +1112,9 @@
   // The last published theme color.
   SkColor last_sent_theme_color_;
 
+  // Whether the first visually non-empty paint has occurred.
+  bool did_first_visually_non_empty_paint_;
+
   // Data for misc internal state ----------------------------------------------
 
   // When > 0, the WebContents is currently being captured (e.g., for