Code: void CastConfigDelegateChromeos::StopCasting(const std::string& activity_id) {
   ExecuteJavaScript("backgroundSetup.stopCastMirroring('user-stop');");
 }

Vulnerability Type: XSS 
CWE ID: CWE-79
Summary: Cross-site scripting (XSS) vulnerability in the DocumentLoader::maybeCreateArchive function in core/loader/DocumentLoader.cpp in Blink, as used in Google Chrome before 35.0.1916.114, allows remote attackers to inject arbitrary web script or HTML via crafted MHTML content, aka *Universal XSS (UXSS).*
Commit Message: Allow the cast tray to function as expected when the installed extension is missing API methods.

BUG=489445

Review URL: https://codereview.chromium.org/1145833003

Cr-Commit-Position: refs/heads/master@{#330663}