Revert "Disable flaky test testPendingUpdateFileDeletedAfterUpdateCompletion"

This reverts commit 50c337ce.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> Disable flaky test testPendingUpdateFileDeletedAfterUpdateCompletion
> 
> TBR=pkotwicz@chromium.org
> NOTRY=true
> 
> Bug: 937109
> Change-Id: I877a311f3256b88a667ff8224904e2fe71acb30b
> Reviewed-on: https://chromium-review.googlesource.com/c/1496767
> Reviewed-by: Yi Gu <yigu@chromium.org>
> Commit-Queue: Yi Gu <yigu@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#636812}

TBR=pkotwicz@chromium.org,yigu@chromium.org

Change-Id: I6d4183a9d42acc43566506e23b863bfd439b8033
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 937109
Reviewed-on: https://chromium-review.googlesource.com/c/1496163Reviewed-by: Yi Gu <yigu@chromium.org>
Commit-Queue: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636815}

chrome/android/junit/src/org/chromium/chrome/browser/webapps/WebApkUpdateManagerUnitTest.java

@@ -527,9 +527,7 @@ public class WebApkUpdateManagerUnitTest {
      * Test that the pending update file is deleted after update completes regardless of whether
      * update succeeded.
      */
-    // @Test
-    // Test flaky. See https://crbug.com/937109.
-    @DisabledTest
+    @Test
     public void testPendingUpdateFileDeletedAfterUpdateCompletion() {
         mClockRule.advance(WebappDataStorage.UPDATE_INTERVAL);