[cc] facilitate use of BeginFrameAcks in tests.

cc/output/begin_frame_args.cc

 // Copyright 2013 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/output/begin_frame_args.h"
 
 #include "base/trace_event/trace_event_argument.h"
 
 namespace cc {
 
@@ skipping 30 matching lines @@
                                base::TimeTicks deadline,
                                base::TimeDelta interval,
                                BeginFrameArgs::BeginFrameArgsType type)
     : frame_time(frame_time),
       deadline(deadline),
       interval(interval),
       sequence_number(sequence_number),
       source_id(source_id),
       type(type),
       on_critical_path(true) {
-  DCHECK_LT(kInvalidFrameNumber, sequence_number);
+  DCHECK_LE(kStartingFrameNumber, sequence_number);
 }
 
 BeginFrameArgs BeginFrameArgs::Create(BeginFrameArgs::CreationLocation location,
                                       uint32_t source_id,
                                       uint64_t sequence_number,
                                       base::TimeTicks frame_time,
                                       base::TimeTicks deadline,
                                       base::TimeDelta interval,
                                       BeginFrameArgs::BeginFrameArgsType type) {
   DCHECK_NE(type, BeginFrameArgs::INVALID);
@@ skipping 59 matching lines @@
                              bool has_damage)
     : sequence_number(sequence_number),
       latest_confirmed_sequence_number(latest_confirmed_sequence_number),
       source_id(source_id),
       remaining_frames(remaining_frames),
       has_damage(has_damage) {
   DCHECK_LT(BeginFrameArgs::kInvalidFrameNumber, sequence_number);
 }
 
 }  // namespace cc