[cronet] Deflake BidirectionalStreamTest#testFlushData

This CL gets rid of the dependency on setAutoAdvance(false), which
might have disabled the reading of data.

If reading of data is paused during the time mAutoAdvance = false,
when we set mAutoAdvance to true, startNextRead() won't be called
automatically. If we don't startNextRead(), Callback#onSucceeded()
will not be called.

Bug: 751700
Cq-Include-Trybots: master.tryserver.chromium.android:android_cronet_tester
Change-Id: I47fa37fb5d71c4ec0fcda5d6fd2ff762c08505d5
Reviewed-on: https://chromium-review.googlesource.com/598992Reviewed-by: Paul Jensen <pauljensen@chromium.org>
Commit-Queue: Helen Li <xunjieli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#492015}

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

@@ -312,9 +312,17 @@ public class BidirectionalStreamTest extends CronetTestBase {
     // before it is called, and it doesn't flush buffers in mPendingQueue.
     public void testFlushData() throws Exception {
         String url = Http2TestServer.getEchoStreamUrl();
+        final ConditionVariable waitOnStreamReady = new ConditionVariable();
         TestBidirectionalStreamCallback callback = new TestBidirectionalStreamCallback() {
             // Number of onWriteCompleted callbacks that have been invoked.
             private int mNumWriteCompleted = 0;
+
+            @Override
+            public void onStreamReady(BidirectionalStream stream) {
+                mResponseStep = ResponseStep.ON_STREAM_READY;
+                waitOnStreamReady.open();
+            }
+
             @Override
             public void onWriteCompleted(BidirectionalStream stream, UrlResponseInfo info,
                     ByteBuffer buffer, boolean endOfStream) {
@@ -365,9 +373,8 @@ public class BidirectionalStreamTest extends CronetTestBase {
                         .addHeader("empty", "")
                         .addHeader("Content-Type", "zebra")
                         .build();
-        callback.setAutoAdvance(false);
         stream.start();
-        callback.waitForNextWriteStep(); // onStreamReady
+        waitOnStreamReady.block();
 
         assertEquals(0, stream.getPendingDataForTesting().size());
         assertEquals(0, stream.getFlushDataForTesting().size());
@@ -379,7 +386,6 @@ public class BidirectionalStreamTest extends CronetTestBase {
         // Write 6, but do not flush. 6 will be in pending queue.
         callback.startNextWrite(stream);
 
-        callback.setAutoAdvance(true);
         callback.blockForDone();
         assertEquals(200, callback.mResponseInfo.getHttpStatusCode());
         assertEquals("123456", callback.mResponseAsString);