Revert of cc: Adding BeginFrameTracker object and removing Now() from LTHI.

cc/scheduler/begin_frame_tracker.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_SCHEDULER_BEGIN_FRAME_TRACKER_H_
-#define CC_SCHEDULER_BEGIN_FRAME_TRACKER_H_
-
-#include <set>
-#include <string>
-
-#include "base/location.h"
-#include "base/trace_event/trace_event.h"
-#include "base/trace_event/trace_event_argument.h"
-#include "cc/output/begin_frame_args.h"
-
-#define BEGINFRAMETRACKER_FROM_HERE FROM_HERE_WITH_EXPLICIT_FUNCTION("")
-
-namespace cc {
-
-// Microclass to trace and check properties for correct BeginFrameArgs (BFA)
-// usage and provide a few helper methods.
-//
-// With DCHECKs enable, this class checks the following "invariants";
-//  * BFA are monotonically increasing.
-//  * BFA is valid.
-//  * The BFA is only used inside a given period.
-//  * A new BFA isn't used before the last BFA is finished with.
-//
-// With the tracing category "cc.debug.scheduler.frames" enabled the tracker
-// will output the following trace information;
-//  * Time period for which the BFA is in usage.
-//  * The flow of BFA as they are passed between tracking objects.
-//
-// TODO(mithro): Record stats about the BeginFrameArgs
-class CC_EXPORT BeginFrameTracker {
- public:
-  explicit BeginFrameTracker(const tracked_objects::Location& location);
-  ~BeginFrameTracker();
-
-  // The Start and Finish methods manage the period that a BFA should be
-  // accessed for. This allows tight control over the BFA and prevents
-  // accidental usage in the wrong period when code is split across multiple
-  // locations.
-
-  // Start using a new BFA value and check invariant properties.
-  // **Must** only be called after finishing with any previous BFA.
-  void Start(BeginFrameArgs new_args);
-  // Finish using the current BFA.
-  // **Must** only be called while still using a BFA.
-  void Finish();
-
-  // The two accessors methods allow access to the BFA stored inside the
-  // tracker. They are mutually exclusive, at any time it is only valid to call
-  // one or the other. This makes sure you understand exactly which BFA you are
-  // intending to use and verifies that is the case.
-
-  // Get the current BFA object.
-  // **Must** only be called between the start and finish methods calls.
-  const BeginFrameArgs& Current() const;
-  // Get the last used BFA.
-  // **Must** only be called when **not** between the start and finish method
-  // calls.
-  const BeginFrameArgs& Last() const;
-
-  // Helper method to try and return a valid interval property. Defaults to
-  // BFA::DefaultInterval() is no other interval can be found. Can be called at
-  // any time.
-  base::TimeDelta Interval() const;
-
-  void AsValueInto(base::TimeTicks now,
-                   base::trace_event::TracedValue* dict) const;
-
-  // The following methods violate principles of how BeginFrameArgs should be
-  // used. These methods should only be used when there is no other choice.
-  bool DangerousMethodHasStarted() const {
-    return !current_updated_at_.is_null();
-  }
-  bool DangerousMethodHasFinished() const { return HasFinished(); }
-  const BeginFrameArgs& DangerousMethodCurrentOrLast() const;
-
- private:
-  // Return if currently not between the start/end period. This method should
-  // be used extremely sparingly and normal indicates incorrect management of
-  // the BFA object. Can be called at any time.
-  bool HasFinished() const { return !current_finished_at_.is_null(); }
-
-  const tracked_objects::Location location_;
-  const std::string location_string_;
-
-  base::TimeTicks current_updated_at_;
-  BeginFrameArgs current_args_;
-  base::TimeTicks current_finished_at_;
-};
-
-}  // namespace cc
-
-#endif  // CC_SCHEDULER_BEGIN_FRAME_TRACKER_H_