Provision to start base::SimpleTestTickClock at initial ticks

cc/scheduler/begin_frame_source_unittest.cc

Index: cc/scheduler/begin_frame_source_unittest.cc
diff --git a/cc/scheduler/begin_frame_source_unittest.cc b/cc/scheduler/begin_frame_source_unittest.cc
index 1f85622878e91680efd7f5ea56402c3653d81ada..5114e639f163dd83ac5b1e36761b0043b77c65f3 100644
--- a/cc/scheduler/begin_frame_source_unittest.cc
+++ b/cc/scheduler/begin_frame_source_unittest.cc
@@ -342,8 +342,8 @@ class BackToBackBeginFrameSourceTest : public ::testing::Test {
   scoped_ptr<MockBeginFrameObserver> obs_;
 
   void SetUp() override {
-    now_src_.reset(new base::SimpleTestTickClock());
-    now_src_->Advance(base::TimeDelta::FromMicroseconds(1000));
+    now_src_.reset(new base::SimpleTestTickClock(
+        base::TimeTicks() + base::TimeDelta::FromMicroseconds(1000)));
     task_runner_ =
         make_scoped_refptr(new OrderedSimpleTaskRunner(now_src_.get(), false));
     task_runner_->SetRunTaskLimit(1);
@@ -509,8 +509,8 @@ class SyntheticBeginFrameSourceTest : public ::testing::Test {
   scoped_ptr<MockBeginFrameObserver> obs_;
 
   void SetUp() override {
-    now_src_.reset(new base::SimpleTestTickClock());
-    now_src_->Advance(base::TimeDelta::FromMicroseconds(1000));
+    now_src_.reset(new base::SimpleTestTickClock(
+        base::TimeTicks() + base::TimeDelta::FromMicroseconds(1000)));
     task_runner_ =
         make_scoped_refptr(new OrderedSimpleTaskRunner(now_src_.get(), false));
     source_ = TestSyntheticBeginFrameSource::Create(