Add @RetryOnFailure to flaky DownloadActivityTest#testSpaceDisplay

BUG=751492
TBR=twellington@chromium.org

Change-Id: Ia823694259de8e88ac1f121fafcf9393b821472b
Reviewed-on: https://chromium-review.googlesource.com/597767Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491345}

chrome/android/javatests/src/org/chromium/chrome/browser/download/DownloadActivityTest.java

@@ -151,6 +151,7 @@ public class DownloadActivityTest extends BaseActivityInstrumentationTestCase<Do
     }
 
     @MediumTest
+    @RetryOnFailure
     public void testSpaceDisplay() throws Exception {
         // This first check is a Criteria because initialization of the Adapter is asynchronous.
         CriteriaHelper.pollUiThread(new Criteria() {