Cancel JavaScript dialogs when an interstitial appears.

BUG=295695
TEST=See bug for repro steps.

Review URL: https://chromiumcodereview.appspot.com/24360011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225026 0039d316-1c4b-4281-b951-d872f2087c98
bool WebContentsImpl::IsSavable() {
  return contents_mime_type_ == "text/html" ||
         contents_mime_type_ == "text/xml" ||
         contents_mime_type_ == "application/xhtml+xml" ||
         contents_mime_type_ == "text/plain" ||
         contents_mime_type_ == "text/css" ||
         net::IsSupportedJavascriptMimeType(contents_mime_type_.c_str());
}

bool WebContentsImpl::IsSavable() {
  return contents_mime_type_ == "text/html" ||
         contents_mime_type_ == "text/xml" ||
         contents_mime_type_ == "application/xhtml+xml" ||
         contents_mime_type_ == "text/plain" ||
         contents_mime_type_ == "text/css" ||
         net::IsSupportedJavascriptMimeType(contents_mime_type_.c_str());
}
