Fix for chrome://cast getting blocked by content security policy.

The provided policy for the cast UI was "object-src *", which used to
include "chrome:" until a recent CL changed the use of “*” from a
blacklist (that did not include "chrome:") to a whitelist (that still does
not include "chrome:"). Because of this, the policy just needs to be updated
to specifically allow "chrome:" now.

BUG=634168

Review-Url: https://codereview.chromium.org/2347503002
Cr-Commit-Position: refs/heads/master@{#418883}

chrome/browser/ui/webui/cast/cast_ui.cc

@@ -32,7 +32,7 @@ CastUI::CastUI(content::WebUI* web_ui)
   html_source->AddString("extensionId", extension_id);
   html_source->SetJsonPath("strings.js");
   html_source->SetDefaultResource(IDR_CAST_HTML);
-  html_source->OverrideContentSecurityPolicyObjectSrc("object-src *;");
+  html_source->OverrideContentSecurityPolicyObjectSrc("object-src * chrome:;");
 
   content::WebUIDataSource::Add(Profile::FromWebUI(web_ui), html_source);
 }