Avoid DCHECK in ExternalBeginFrameSource::GetMissedBeginFrameArgs caused by out of order frame time

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 555 matching lines @@
 
   // 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);
 }
 
+// https://crbug.com/730218: Avoid DCHECK crash in
+// ExternalBeginFrameSource::GetMissedBeginFrameArgs.
+TEST_F(ExternalBeginFrameSourceTest, GetMissedBeginFrameArgs) {
+  BeginFrameArgs args = CreateBeginFrameArgsForTesting(BEGINFRAME_FROM_HERE, 0,
+                                                       2, 10000, 10100, 100);
+  source_->OnBeginFrame(args);
+
+  EXPECT_BEGIN_FRAME_SOURCE_PAUSED(*obs_, false);
+  EXPECT_BEGIN_FRAME_USED_MISSED(*obs_, 0, 2, 10000, 10100, 100);
+  source_->AddObserver(obs_.get());
+  source_->RemoveObserver(obs_.get());
+
+  // Out of order frame_time. This might not be valid but still shouldn't
+  // cause a DCHECK in ExternalBeginFrameSource code.
+  args = CreateBeginFrameArgsForTesting(BEGINFRAME_FROM_HERE, 0, 2, 9999, 10100,
+                                        101);
+  source_->OnBeginFrame(args);
+
+  EXPECT_CALL((*client_), OnNeedsBeginFrames(true)).Times(1);
+  EXPECT_BEGIN_FRAME_SOURCE_PAUSED(*obs_, false);
+  EXPECT_CALL(*obs_, OnBeginFrame(CreateBeginFrameArgsForTesting(

[sunnyps, 2017/06/07 23:22:24]

nit: EXPECT_CALL(*obs_, _) instead? We don't want any begin frame no matter how
the args are calculated.

[stanisc, 2017/06/07 23:36:33]

Done. I tried that initially but couldn't make it work because I was
missing a using statement at the top.

+                         BEGINFRAME_FROM_HERE, 0, 1, 9999, 10100, 101)))
+      .Times(0);
+  source_->AddObserver(obs_.get());
+}
+
 }  // namespace
 }  // namespace cc