[cc] Add test for ExternalBFS::OnBeginFrame continuity check.

cc/scheduler/begin_frame_source_unittest.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/scheduler/begin_frame_source.h"
 
 #include <stdint.h>
 
 #include "base/memory/ptr_util.h"
 #include "base/test/test_simple_task_runner.h"
@@ skipping 865 matching lines @@
       BEGINFRAME_FROM_HERE, 0, 2, base::TimeTicks::FromInternalValue(10000));
   EXPECT_BEGIN_FRAME_ARGS_USED(*obs_, args);
   source_->OnBeginFrame(args);
 
   EXPECT_CALL((*client_), OnDidFinishFrame(BeginFrameAck(0, 2, 2, 0, false)))
       .Times(1);
   EXPECT_CALL((*client_), OnNeedsBeginFrames(false)).Times(1);
   source_->RemoveObserver(obs_.get());
 }
 
+// https://crbug.com/690127: Duplicate BeginFrame caused DCHECK crash.
+TEST_F(ExternalBeginFrameSourceTest, OnBeginFrameChecksBeginFrameContinuity) {
+  EXPECT_BEGIN_FRAME_SOURCE_PAUSED(*obs_, false);
+  EXPECT_CALL((*client_), OnNeedsBeginFrames(true)).Times(1);
+  source_->AddObserver(obs_.get());
+
+  BeginFrameArgs args = CreateBeginFrameArgsForTesting(
+      BEGINFRAME_FROM_HERE, 0, 2, base::TimeTicks::FromInternalValue(10000));
+  EXPECT_BEGIN_FRAME_ARGS_USED(*obs_, args);
+  source_->OnBeginFrame(args);
+
+  // Providing same args again to OnBeginFrame() should not notify observer.
+  EXPECT_CALL((*client_), OnDidFinishFrame(BeginFrameAck(0, 2, 0, 0, false)))
+      .Times(1);
+  source_->OnBeginFrame(args);
+
+  // Providing same args through a different ExternalBeginFrameSource also does
+  // not notify observer.
+  EXPECT_BEGIN_FRAME_SOURCE_PAUSED(*obs_, false);
+  EXPECT_CALL((*client_), OnNeedsBeginFrames(true)).Times(1);
+  ExternalBeginFrameSource source2(client_.get());
+  source2.AddObserver(obs_.get());
+  source2.OnBeginFrame(args);
+}
+
 }  // namespace
 }  // namespace cc