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

cc/scheduler/scheduler_unittest.cc

Index: cc/scheduler/scheduler_unittest.cc
diff --git a/cc/scheduler/scheduler_unittest.cc b/cc/scheduler/scheduler_unittest.cc
index f8a9d3fc68c2e657e4ee3bbd02a18f9cb07df092..eaa013861fb9263ed3d4b96fa383bb5a64b0547b 100644
--- a/cc/scheduler/scheduler_unittest.cc
+++ b/cc/scheduler/scheduler_unittest.cc
@@ -2916,16 +2916,14 @@ TEST_F(SchedulerTest, SynchronousCompositorDoubleCommitWithoutDraw) {
 
 TEST_F(SchedulerTest, AuthoritativeVSyncInterval) {
   SetUpScheduler(true);
-
-  base::TimeDelta initial_interval =
-      scheduler_->begin_impl_frame_args().interval;
+  base::TimeDelta initial_interval = scheduler_->BeginImplFrameInterval();
   base::TimeDelta authoritative_interval =
       base::TimeDelta::FromMilliseconds(33);
 
   scheduler_->SetNeedsCommit();
   EXPECT_SCOPED(AdvanceFrame());
 
-  EXPECT_EQ(initial_interval, scheduler_->begin_impl_frame_args().interval);
+  EXPECT_EQ(initial_interval, scheduler_->BeginImplFrameInterval());
 
   scheduler_->NotifyBeginMainFrameStarted();
   scheduler_->NotifyReadyToCommit();
@@ -2937,9 +2935,8 @@ TEST_F(SchedulerTest, AuthoritativeVSyncInterval) {
 
   // At the next BeginFrame, authoritative interval is used instead of previous
   // interval.
-  EXPECT_NE(initial_interval, scheduler_->begin_impl_frame_args().interval);
-  EXPECT_EQ(authoritative_interval,
-            scheduler_->begin_impl_frame_args().interval);
+  EXPECT_NE(initial_interval, scheduler_->BeginImplFrameInterval());
+  EXPECT_EQ(authoritative_interval, scheduler_->BeginImplFrameInterval());
 }
 
 }  // namespace