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..0065aead9e37760e4a80bda08db126ff5dfaebc3 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, bool lazy_disable) {
+  return make_scoped_refptr(new VSyncTimeSource(vsync_provider, lazy_disable));
 }
 
-VSyncTimeSource::VSyncTimeSource(VSyncProvider* vsync_provider)
+VSyncTimeSource::VSyncTimeSource(
+    VSyncProvider* vsync_provider, bool lazy_disable)
     : active_(false),
       notification_requested_(false),
       vsync_provider_(vsync_provider),
-      client_(NULL) {}
+      client_(NULL),
+      lazy_disable_(lazy_disable) {}
 
 VSyncTimeSource::~VSyncTimeSource() {}
 
@@ -34,6 +38,10 @@ void VSyncTimeSource::SetActive(bool active) {
     notification_requested_ = true;
     vsync_provider_->RequestVSyncNotification(this);
   }
+  if (!active_ && !lazy_disable_) {
+    notification_requested_ = false;
+    vsync_provider_->RequestVSyncNotification(NULL);
+  }
 }
 
 bool VSyncTimeSource::Active() const {
@@ -55,7 +63,9 @@ void VSyncTimeSource::SetTimebaseAndInterval(base::TimeTicks,
 
 void VSyncTimeSource::DidVSync(base::TimeTicks frame_time) {
   last_tick_time_ = frame_time;
-  if (!active_) {
+  if (!lazy_disable_) {
+    DCHECK(active_);
+  } else if (!active_) {
     if (notification_requested_) {
       notification_requested_ = false;
       vsync_provider_->RequestVSyncNotification(NULL);