Fix ChromeActivityTestCaseBase tearDown mistake

In the JUnit4 conversion CL (https://codereview.chromium.org/2815453003)
super.tearDown() call was mistakenly removed.

BUG=718454

Review-Url: https://codereview.chromium.org/2861433006
Cr-Commit-Position: refs/heads/master@{#469379}

chrome/test/android/javatests/src/org/chromium/chrome/test/ChromeActivityTestCaseBase.java

@@ -59,6 +59,7 @@ public abstract class ChromeActivityTestCaseBase<T extends ChromeActivity>
     @Override
     protected void tearDown() throws Exception {
         mTestCommon.tearDown();
+        super.tearDown();
     }
 
     /**