Add LayerTreeHostSettings for synchronous compositor

cc/scheduler/vsync_time_source.cc

Index: cc/scheduler/vsync_time_source.cc
diff --git a/cc/scheduler/vsync_time_source.cc b/cc/scheduler/vsync_time_source.cc
index 75314fbeff76e7a9477239d69d7292ab6c491f4e..206e2376675156e36cd20ee0d284a7dc40b5f7ab 100644
--- a/cc/scheduler/vsync_time_source.cc
+++ b/cc/scheduler/vsync_time_source.cc
@@ -4,18 +4,22 @@
 
 #include "cc/scheduler/vsync_time_source.h"
 
+#include "base/logging.h"
+
 namespace cc {
 
 scoped_refptr<VSyncTimeSource> VSyncTimeSource::Create(
-    VSyncProvider* vsync_provider) {
-  return make_scoped_refptr(new VSyncTimeSource(vsync_provider));
+    VSyncProvider* vsync_provider, NotificationDisableOption option) {
+  return make_scoped_refptr(new VSyncTimeSource(vsync_provider, option));
 }
 
-VSyncTimeSource::VSyncTimeSource(VSyncProvider* vsync_provider)
+VSyncTimeSource::VSyncTimeSource(
+    VSyncProvider* vsync_provider, NotificationDisableOption option)
     : active_(false),
       notification_requested_(false),
       vsync_provider_(vsync_provider),
-      client_(NULL) {}
+      client_(NULL),
+      disable_option_(option) {}
 
 VSyncTimeSource::~VSyncTimeSource() {}
 
@@ -27,13 +31,14 @@ void VSyncTimeSource::SetActive(bool active) {
   if (active_ == active)
     return;
   active_ = active;
-  // The notification will be lazily disabled in the callback to ensure
-  // we get notified of the frame immediately following a quick on-off-on
-  // transition.
   if (active_ && !notification_requested_) {
     notification_requested_ = true;
     vsync_provider_->RequestVSyncNotification(this);
   }
+  if (!active_ && disable_option_ == DISABLE_SYNCHRONOUSLY) {
+    notification_requested_ = false;
+    vsync_provider_->RequestVSyncNotification(NULL);
+  }
 }
 
 bool VSyncTimeSource::Active() const {
@@ -55,7 +60,9 @@ void VSyncTimeSource::SetTimebaseAndInterval(base::TimeTicks,
 
 void VSyncTimeSource::DidVSync(base::TimeTicks frame_time) {
   last_tick_time_ = frame_time;
-  if (!active_) {
+  if (disable_option_ == DISABLE_SYNCHRONOUSLY) {
+    DCHECK(active_);
+  } else if (!active_) {
     if (notification_requested_) {
       notification_requested_ = false;
       vsync_provider_->RequestVSyncNotification(NULL);