throw RuntimeException if failed to stop a timedout site

this situation usually happens when WebView is spinning or
deadlocked on something, throwing a RuntimeException will
make this kind of error more noticeable

Change-Id: Id2f495494f67206830fd9d9e8a4bc2b175e82614
diff --git a/tests/src/com/android/browser/PopularUrlsTest.java b/tests/src/com/android/browser/PopularUrlsTest.java
index e407194..5e367be 100644
--- a/tests/src/com/android/browser/PopularUrlsTest.java
+++ b/tests/src/com/android/browser/PopularUrlsTest.java
@@ -294,7 +294,7 @@
             // try to wait for count down latch again
             timedout = !mLatch.await(5000, TimeUnit.MILLISECONDS);
             if (timedout) {
-                Log.e(TAG, "failed to stop the timedout site in 5s");
+                throw new RuntimeException("failed to stop timedout site, is browser pegged?");
             }
         }
     }