Fix CronetUrlRequestTest#testFailures flake

When CronetUrlRequest is canceled asynchronously in a callback without
being paused, we might already have a onSucceeded() callback in the
executor's queue. If that is the case, we won't have a onCanceled()
callback. This led to test flake. This CL adjusts the test expectation
and adds a comment.

R=pauljensen@chromium.org

BUG=657415
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_cronet_tester

Review-Url: https://codereview.chromium.org/2572693003
Cr-Commit-Position: refs/heads/master@{#438526}

components/cronet/android/test/javatests/src/org/chromium/net/CronetUrlRequestTest.java

@@ -1679,10 +1679,16 @@ public class CronetUrlRequestTest extends CronetTestBase {
         assertEquals(expectResponseInfo, callback.mResponseInfo != null);
         assertEquals(expectError, callback.mError != null);
         assertEquals(expectError, callback.mOnErrorCalled);
-        assertEquals(failureType == FailureType.CANCEL_SYNC
-                        || failureType == FailureType.CANCEL_ASYNC
-                        || failureType == FailureType.CANCEL_ASYNC_WITHOUT_PAUSE,
-                callback.mOnCanceledCalled);
+        // When failureType is FailureType.CANCEL_ASYNC_WITHOUT_PAUSE and failureStep is
+        // ResponseStep.ON_READ_COMPLETED, there might be an onSucceeded() task already posted. If
+        // that's the case, onCanceled() will not be invoked. See crbug.com/657415.
+        if (!(failureType == FailureType.CANCEL_ASYNC_WITHOUT_PAUSE
+                    && failureStep == ResponseStep.ON_READ_COMPLETED)) {
+            assertEquals(failureType == FailureType.CANCEL_SYNC
+                            || failureType == FailureType.CANCEL_ASYNC
+                            || failureType == FailureType.CANCEL_ASYNC_WITHOUT_PAUSE,
+                    callback.mOnCanceledCalled);
+        }
     }
 
     @SmallTest