Provision to start base::SimpleTestTickClock at initial ticks

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 <deque>
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/gtest_prod_util.h"
 #include "base/test/test_simple_task_runner.h"
@@ skipping 325 matching lines @@
   static const int64_t kDeadline;
   static const int64_t kInterval;
 
   scoped_ptr<base::SimpleTestTickClock> now_src_;
   scoped_refptr<OrderedSimpleTaskRunner> task_runner_;
   scoped_ptr<TestBackToBackBeginFrameSource> source_;
   scoped_ptr<MockBeginFrameObserver> obs_;
 
   void SetUp() override {
     now_src_.reset(new base::SimpleTestTickClock());
-    now_src_->Advance(base::TimeDelta::FromMicroseconds(1000));
+    // SimpleTestTickClock starts at 1 microsecond, advance to 1000
+    now_src_->Advance(base::TimeDelta::FromMicroseconds(999));

[Sami, 2015/06/18 20:57:43]

It feels like having two constructor for SimpleTestTickClock would help to avoid
cases like these. One would initialize it to zero and the other would take a
TimeTicks value to initialize to. WDYT?

[Ankur Verma, 2015/06/30 09:19:26]

Done.

     task_runner_ =
         make_scoped_refptr(new OrderedSimpleTaskRunner(now_src_.get(), false));
     task_runner_->SetRunTaskLimit(1);
     source_ = TestBackToBackBeginFrameSource::Create(now_src_.get(),
                                                      task_runner_.get());
     obs_ = make_scoped_ptr(new ::testing::StrictMock<MockBeginFrameObserver>());
     source_->AddObserver(obs_.get());
   }
 
   void TearDown() override { obs_.reset(); }
@@ skipping 413 matching lines @@
   mux_->SetActiveSource(source2_);
   SEND_BEGIN_FRAME_DROP(*source2_, 750, 1050, 300);
   SEND_BEGIN_FRAME_USED(*source2_, 1050, 1250, 300);
 
   mux_->SetActiveSource(source1_);
   SEND_BEGIN_FRAME_DROP(*source2_, 1100, 1400, 300);
 }
 
 }  // namespace
 }  // namespace cc