Don't allow sending data URLs to WebUI, unless in a ChromeOS BalloonHost.

content/public/browser/web_contents_delegate.h

Index: content/public/browser/web_contents_delegate.h
diff --git a/content/public/browser/web_contents_delegate.h b/content/public/browser/web_contents_delegate.h
index 682b3843843795f51ab7d67af3ecd34fec234e9a..b99890b927cab7e35d30dd2322ebf817135aebb4 100644
--- a/content/public/browser/web_contents_delegate.h
+++ b/content/public/browser/web_contents_delegate.h
@@ -157,6 +157,10 @@ class CONTENT_EXPORT WebContentsDelegate {
   // application.
   virtual bool IsApplication() const;
 
+  // Check whether this contents is permitted to load data URLs in WebUI mode.
+  // This is normally disallowed for security.
+  virtual bool CanLoadDataURLsInWebUI() const;
+
   // Detach the given tab and convert it to a "webapp" view.  The tab must be
   // a WebContents with a valid WebApp set.
   virtual void ConvertContentsToApplication(WebContents* source) {}