Use const reference for argument of BeginFrameTracker::Start()

This avoids a copy of viz::BeginFrameArgs for the argument.
sizeof(viz::BeginFrameArgs) is 56 on LP64 systems.

Change-Id: I2d0c99ae490824563907cdfbe86b5196f3015936
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2146784
Commit-Queue: vmpstr <vmpstr@chromium.org>
Reviewed-by: vmpstr <vmpstr@chromium.org>
Auto-Submit: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#758840}

cc/scheduler/begin_frame_tracker.cc

@@ -16,7 +16,7 @@ BeginFrameTracker::BeginFrameTracker(const base::Location& location)
 
 BeginFrameTracker::~BeginFrameTracker() = default;
 
-void BeginFrameTracker::Start(viz::BeginFrameArgs new_args) {
+void BeginFrameTracker::Start(const viz::BeginFrameArgs& new_args) {
   // Trace the frame time being passed between BeginFrameTrackers.
   TRACE_EVENT_FLOW_STEP0(
       TRACE_DISABLED_BY_DEFAULT("cc.debug.scheduler.frames"), "BeginFrameArgs",

cc/scheduler/begin_frame_tracker.h

@@ -49,7 +49,7 @@ class CC_EXPORT BeginFrameTracker {
 
   // Start using a new BFA value and check invariant properties.
   // **Must** only be called after finishing with any previous BFA.
-  void Start(viz::BeginFrameArgs new_args);
+  void Start(const viz::BeginFrameArgs& new_args);
   // Finish using the current BFA.
   // **Must** only be called while still using a BFA.
   void Finish();