aw: Enable testMediaPlaybackWithUserGesture

BUG=396645

Review URL: https://codereview.chromium.org/557433002

Cr-Commit-Position: refs/heads/master@{#293796}

android_webview/javatests/src/org/chromium/android_webview/test/AwSettingsTest.java

@@ -2714,12 +2714,8 @@ public class AwSettingsTest extends AwTestBase {
         assertTrue(VideoTestUtil.runVideoTest(this, false, WAIT_TIMEOUT_MS));
     }
 
-    /*
     @SmallTest
     @Feature({"AndroidWebView", "Preferences"})
-    http://crbug.com/396645
-    */
-    @DisabledTest
     public void testMediaPlaybackWithUserGesture() throws Throwable {
         // Wait for 5 second to see if video played.
         assertFalse(VideoTestUtil.runVideoTest(this, true, scaleTimeout(5000)));