[cc]: Add a BeginMainFrameNotExpectedSoon signal and route it to the RendererScheduler.

content/renderer/scheduler/null_renderer_scheduler.cc

Index: content/renderer/scheduler/null_renderer_scheduler.cc
diff --git a/content/renderer/scheduler/null_renderer_scheduler.cc b/content/renderer/scheduler/null_renderer_scheduler.cc
index 2c35bd3dbb0c1cf5cf3af81ef6f5b5e6c8df93f7..453b5889d2810e888a0a7673bdc66cf5ebdeef3a 100644
--- a/content/renderer/scheduler/null_renderer_scheduler.cc
+++ b/content/renderer/scheduler/null_renderer_scheduler.cc
@@ -68,6 +68,9 @@ NullRendererScheduler::IdleTaskRunner() {
 void NullRendererScheduler::WillBeginFrame(const cc::BeginFrameArgs& args) {
 }
 
+void NullRendererScheduler::BeginFrameNoLongerRequired() {
+}
+
 void NullRendererScheduler::DidCommitFrameToCompositor() {
 }