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

content/public/browser/web_contents_delegate.cc

Index: content/public/browser/web_contents_delegate.cc
diff --git a/content/public/browser/web_contents_delegate.cc b/content/public/browser/web_contents_delegate.cc
index f4c0bc970380e7bfbe1da845d6eaca8930494df5..0c115485373aada775881c693013dc578da3d0aa 100644
--- a/content/public/browser/web_contents_delegate.cc
+++ b/content/public/browser/web_contents_delegate.cc
@@ -30,6 +30,8 @@ bool WebContentsDelegate::IsPopupOrPanel(const WebContents* source) const {
 
 bool WebContentsDelegate::IsApplication() const { return false; }
 
+bool WebContentsDelegate::CanLoadDataURLsInWebUI() const { return false; }
+
 bool WebContentsDelegate::CanReloadContents(WebContents* source) const {
   return true;
 }