Mac Overlays: Add GPU back-pressure

ui/accelerated_widget_mac/display_link_mac.cc

Index: ui/accelerated_widget_mac/display_link_mac.cc
diff --git a/ui/accelerated_widget_mac/display_link_mac.cc b/ui/accelerated_widget_mac/display_link_mac.cc
index c9a30699a06fff31a5b8117c2cfb7f5d7b64e0c6..3013efb58e9469864717da37468c9117d2854ded 100644
--- a/ui/accelerated_widget_mac/display_link_mac.cc
+++ b/ui/accelerated_widget_mac/display_link_mac.cc
@@ -27,6 +27,9 @@ namespace ui {
 // static
 scoped_refptr<DisplayLinkMac> DisplayLinkMac::GetForDisplay(
     CGDirectDisplayID display_id) {
+  if (!display_id)
+    return nullptr;
+
   // Return the existing display link for this display, if it exists.
   DisplayMap::iterator found = display_map_.Get().find(display_id);
   if (found != display_map_.Get().end()) {
@@ -105,6 +108,22 @@ bool DisplayLinkMac::GetVSyncParameters(
   return true;
 }
 
+base::TimeTicks DisplayLinkMac::GetNextVSyncTimeAfter(
+    const base::TimeTicks& from, double interval_fraction) {
+  if (!timebase_and_interval_valid_) {
+    StartOrContinueDisplayLink();
+    return from;
+  }
+
+  // Compute the previous vsync time.
+  base::TimeTicks previous_vsync =
+      interval_ * ((from - timebase_remainder_) / interval_) +
+      timebase_remainder_;
+
+  // Return |interval_fraction| through the next vsync.
+  return previous_vsync + (1 + interval_fraction) * interval_;
+}
+
 void DisplayLinkMac::Tick(const CVTimeStamp& cv_time) {
   TRACE_EVENT0("ui", "DisplayLinkMac::Tick");
 
@@ -123,6 +142,9 @@ void DisplayLinkMac::Tick(const CVTimeStamp& cv_time) {
       cv_time.hostTime / 1000);
   interval_ = base::TimeDelta::FromMicroseconds(
       1000000 * static_cast<int64>(numerator) / denominator);
+  // Compute |timebase_remainder_| to be the first vsync after time zero.
+  timebase_remainder_ =
+      timebase_ - interval_ * ((timebase_ - base::TimeTicks()) / interval_);
   timebase_and_interval_valid_ = true;
 
   StopDisplayLink();