[cc] Calculate the correct latest_confirmed_sequence_number in cc::Scheduler.

cc/test/fake_external_begin_frame_source.h

 // Copyright 2014 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.
 
 #ifndef CC_TEST_FAKE_EXTERNAL_BEGIN_FRAME_SOURCE_H_
 #define CC_TEST_FAKE_EXTERNAL_BEGIN_FRAME_SOURCE_H_
 
 #include <set>
 
 #include "base/cancelable_callback.h"
 #include "base/memory/weak_ptr.h"
 #include "base/threading/non_thread_safe.h"
 #include "cc/output/begin_frame_args.h"
 #include "cc/scheduler/begin_frame_source.h"
 
+namespace base {
+class SimpleTestTickClock;
+}  // namespace base
+
 namespace cc {
 
 class FakeExternalBeginFrameSource
     : public BeginFrameSource,
       public NON_EXPORTED_BASE(base::NonThreadSafe) {
  public:
   class Client {
    public:
     virtual void OnAddObserver(BeginFrameObserver* obs) = 0;
     virtual void OnRemoveObserver(BeginFrameObserver* obs) = 0;
   };
 
   explicit FakeExternalBeginFrameSource(double refresh_rate,
                                         bool tick_automatically);
   ~FakeExternalBeginFrameSource() override;
 
   void SetClient(Client* client) { client_ = client; }
   void SetPaused(bool paused);
 
   // BeginFrameSource implementation.
   void AddObserver(BeginFrameObserver* obs) override;
   void RemoveObserver(BeginFrameObserver* obs) override;
   void DidFinishFrame(BeginFrameObserver* obs,
-                      const BeginFrameAck& ack) override {}
+                      const BeginFrameAck& ack) override;
   bool IsThrottled() const override;
 
+  BeginFrameArgs CreateBeginFrameArgs(
+      BeginFrameArgs::CreationLocation location);
+  BeginFrameArgs CreateBeginFrameArgs(BeginFrameArgs::CreationLocation location,
+                                      base::SimpleTestTickClock* now_src);
+  uint64_t next_begin_frame_number() const { return next_begin_frame_number_; }
+
   void TestOnBeginFrame(const BeginFrameArgs& args);
 
   size_t num_observers() const { return observers_.size(); }
 
+  const BeginFrameAck& LastAckForObserver(BeginFrameObserver* obs) {
+    return last_acks_[obs];
+  }
+
  private:
   void PostTestOnBeginFrame();
 
   const bool tick_automatically_;
   const double milliseconds_per_frame_;
   Client* client_ = nullptr;
   bool paused_ = false;
   BeginFrameArgs current_args_;
   uint64_t next_begin_frame_number_ = BeginFrameArgs::kStartingFrameNumber;
   std::set<BeginFrameObserver*> observers_;
   base::CancelableCallback<void(const BeginFrameArgs&)> begin_frame_task_;
+  std::unordered_map<BeginFrameObserver*, BeginFrameAck> last_acks_;
   base::WeakPtrFactory<FakeExternalBeginFrameSource> weak_ptr_factory_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_FAKE_EXTERNAL_BEGIN_FRAME_SOURCE_H_