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

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index abec01ea496df05eecf176593b53c3a7772ff7ff..57f5084bf9263ccfa9d6dda1cdcae23de26925a5 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -71,7 +71,6 @@
 #include "cc/trees/tree_synchronizer.h"
 #include "gpu/command_buffer/client/gles2_interface.h"
 #include "gpu/GLES2/gl2extchromium.h"
-#include "ui/gfx/frame_time.h"
 #include "ui/gfx/geometry/rect_conversions.h"
 #include "ui/gfx/geometry/size_conversions.h"
 #include "ui/gfx/geometry/vector2d_conversions.h"
@@ -190,6 +189,7 @@ LayerTreeHostImpl::LayerTreeHostImpl(
     int id)
     : client_(client),
       proxy_(proxy),
+      current_begin_frame_tracker_(BEGINFRAMETRACKER_FROM_HERE),
       use_gpu_rasterization_(false),
       gpu_rasterization_status_(GpuRasterizationStatus::OFF_DEVICE),
       input_handler_client_(NULL),
@@ -220,7 +220,6 @@ LayerTreeHostImpl::LayerTreeHostImpl(
       device_scale_factor_(1.f),
       overhang_ui_resource_id_(0),
       resourceless_software_draw_(false),
-      begin_impl_frame_interval_(BeginFrameArgs::DefaultInterval()),
       animation_registrar_(AnimationRegistrar::Create()),
       rendering_stats_instrumentation_(rendering_stats_instrumentation),
       micro_benchmark_controller_(this),
@@ -374,6 +373,9 @@ bool LayerTreeHostImpl::CanDraw() const {
 }
 
 void LayerTreeHostImpl::Animate(base::TimeTicks monotonic_time) {
+  // DCHECK(!current_begin_frame_tracker_.HasFinished());
+  // DCHECK(monotonic_time == current_begin_frame_tracker_.Get().frame_time)
+  //  << "Called animate with unknown frame time!?";
   if (input_handler_client_)
     input_handler_client_->Animate(monotonic_time);
   AnimatePageScale(monotonic_time);
@@ -1633,11 +1635,7 @@ bool LayerTreeHostImpl::SwapBuffers(const LayerTreeHostImpl::FrameData& frame) {
 }
 
 void LayerTreeHostImpl::WillBeginImplFrame(const BeginFrameArgs& args) {
-  // Sample the frame time now. This time will be used for updating animations
-  // when we draw.
-  UpdateCurrentBeginFrameArgs(args);
-  // Cache the begin impl frame interval
-  begin_impl_frame_interval_ = args.interval;
+  current_begin_frame_tracker_.Start(args);
 
   if (required_for_draw_tile_is_top_of_raster_queue_) {
     // Optimistically schedule a draw, as a tile required for draw is at the top
@@ -2410,7 +2408,8 @@ InputHandler::ScrollStatus LayerTreeHostImpl::ScrollAnimated(
 
     curve->UpdateTarget(
         animation->TrimTimeToCurrentIteration(
-                       CurrentBeginFrameArgs().frame_time).InSecondsF(),
+                       current_begin_frame_tracker_.Get().frame_time)
+            .InSecondsF(),
         new_target);
 
     return ScrollStarted;
@@ -3219,28 +3218,21 @@ TreePriority LayerTreeHostImpl::GetTreePriority() const {
   return global_tile_state_.tree_priority;
 }
 
-void LayerTreeHostImpl::UpdateCurrentBeginFrameArgs(
-    const BeginFrameArgs& args) {
-  DCHECK(!current_begin_frame_args_.IsValid());
-  current_begin_frame_args_ = args;
-  // TODO(skyostil): Stop overriding the frame time once the usage of frame
-  // timing is unified.
-  current_begin_frame_args_.frame_time = gfx::FrameTime::Now();
-}
-
 void LayerTreeHostImpl::ResetCurrentBeginFrameArgsForNextFrame() {
-  current_begin_frame_args_ = BeginFrameArgs();
+  current_begin_frame_tracker_.Finish();
 }
 
 BeginFrameArgs LayerTreeHostImpl::CurrentBeginFrameArgs() const {
-  // Try to use the current frame time to keep animations non-jittery.  But if
-  // we're not in a frame (because this is during an input event or a delayed
-  // task), fall back to physical time.  This should still be monotonic.
-  if (current_begin_frame_args_.IsValid())
-    return current_begin_frame_args_;
-  return BeginFrameArgs::Create(
-      BEGINFRAME_FROM_HERE, gfx::FrameTime::Now(), base::TimeTicks(),
-      BeginFrameArgs::DefaultInterval(), BeginFrameArgs::NORMAL);
+  // TODO(mithro): Remove this section once all calls to CurrentBeginFrameArgs
+  // which happens outside frame rendering are fixed.
+  if (current_begin_frame_tracker_.HasFinished()) {
+    return current_begin_frame_tracker_.Last();
+  }
+  return current_begin_frame_tracker_.Get();
+}
+
+base::TimeDelta LayerTreeHostImpl::CurrentBeginFrameInterval() const {
+  return current_begin_frame_tracker_.Interval();
 }
 
 scoped_refptr<base::debug::ConvertableToTraceFormat>