cc: Prioritize impl-thread drawing in scheduler in smoothness mode

When the compositor is in prefer smoothness mode, prioritize impl-thread
draws over main thread frames and tree activations in the scheduler.
This makes it less likely for us to drop frames during
smoothness-triggering gestures such as flings and pinch-zooms. The
tradeoff is that main thread updates will have higher latency in these
modes.

BUG=309630

Review URL: https://codereview.chromium.org/35013002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230141 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 17 insertions, 2 deletions

diff --git a/cc/scheduler/scheduler_state_machine.cc b/cc/scheduler/scheduler_state_machine.cc
index c14186a..227d5ed 100644
--- a/cc/scheduler/scheduler_state_machine.cc
+++ b/cc/scheduler/scheduler_state_machine.cc
@@ -39,7 +39,8 @@ SchedulerStateMachine::SchedulerStateMachine(const SchedulerSettings& settings)
       pending_tree_is_ready_for_activation_(false),
       active_tree_needs_first_draw_(false),
       draw_if_possible_failed_(false),
-      did_create_and_initialize_first_output_surface_(false) {}
+      did_create_and_initialize_first_output_surface_(false),
+      smoothness_takes_priority_(false) {}
 
 const char* SchedulerStateMachine::OutputSurfaceStateToString(
     OutputSurfaceState state) {
@@ -255,6 +256,8 @@ scoped_ptr<base::Value> SchedulerStateMachine::AsValue() const  {
   minor_state->SetBoolean("draw_if_possible_failed", draw_if_possible_failed_);
   minor_state->SetBoolean("did_create_and_initialize_first_output_surface",
                           did_create_and_initialize_first_output_surface_);
+  minor_state->SetBoolean("smoothness_takes_priority",
+                          smoothness_takes_priority_);
   state->Set("minor_state", minor_state.release());
 
   return state.PassAs<base::Value>();
@@ -896,12 +899,19 @@ bool SchedulerStateMachine::ShouldTriggerBeginImplFrameDeadlineEarly() const {
   if (active_tree_needs_first_draw_)
     return true;
 
+  if (!needs_redraw_)
+    return false;
+
   // This is used to prioritize impl-thread draws when the main thread isn't
   // producing anything, e.g., after an aborted commit. We also check that we
   // don't have a pending tree -- otherwise we should give it a chance to
   // activate.
   // TODO(skyostil): Revisit this when we have more accurate deadline estimates.
-  if (commit_state_ == COMMIT_STATE_IDLE && needs_redraw_ && !has_pending_tree_)
+  if (commit_state_ == COMMIT_STATE_IDLE && !has_pending_tree_)
+    return true;
+
+  // Prioritize impl-thread draws in smoothness mode.
+  if (smoothness_takes_priority_)
     return true;
 
   return false;
@@ -935,6 +945,11 @@ void SchedulerStateMachine::SetSwapUsedIncompleteTile(
   swap_used_incomplete_tile_ = used_incomplete_tile;
 }
 
+void SchedulerStateMachine::SetSmoothnessTakesPriority(
+    bool smoothness_takes_priority) {
+  smoothness_takes_priority_ = smoothness_takes_priority;
+}
+
 void SchedulerStateMachine::DidDrawIfPossibleCompleted(bool success) {
   draw_if_possible_failed_ = !success;
   if (draw_if_possible_failed_) {