Revert 264490 "Disabling WebRtcApprtcBrowserTest.MANUAL_FirefoxA..."

> Disabling WebRtcApprtcBrowserTest.MANUAL_FirefoxApprtcInteropTest since it times out and I can't reproduce locally or find any change to blame. Seems flaky and is already disabled on other platforms.
> 
> TBR=vrk
> BUG=364418
> 
> Review URL: https://codereview.chromium.org/240783004

The test seems to be fine as far I can tell; speculative re-enable

TBR=henrika@chromium.org

Review URL: https://codereview.chromium.org/266973003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@268150 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/media/chrome_webrtc_apprtc_browsertest.cc

@@ -217,7 +217,7 @@ IN_PROC_BROWSER_TEST_F(WebRtcApprtcBrowserTest, MANUAL_WorksOnApprtc) {
 }
 
 #if defined(OS_LINUX)
-#define MAYBE_MANUAL_FirefoxApprtcInteropTest DISABLED_MANUAL_FirefoxApprtcInteropTest
+#define MAYBE_MANUAL_FirefoxApprtcInteropTest MANUAL_FirefoxApprtcInteropTest
 #else
 // Not implemented yet on Windows and Mac.
 #define MAYBE_MANUAL_FirefoxApprtcInteropTest DISABLED_MANUAL_FirefoxApprtcInteropTest