Adding tests for new webstore beginInstallWithManifest method.

BUG=75821
TEST=none
Review URL: http://codereview.chromium.org/6900059

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@83080 0039d316-1c4b-4281-b951-d872f2087c98
void WebstorePrivateApi::SetTestingBrowserSignin(BrowserSignin* signin) {
  test_signin = signin;
}

void WebstorePrivateApi::SetTestingBrowserSignin(BrowserSignin* signin) {
  test_signin = signin;
}
