cc: Force layer tree tests to go idle before exiting.

cc/thread_proxy.cc

Index: cc/thread_proxy.cc
diff --git a/cc/thread_proxy.cc b/cc/thread_proxy.cc
index cd0baa3b6aa6dbc3d892f62a2f039722001599bb..4a437bb1adf79648896ffebcb1084b87012b5a81 100644
--- a/cc/thread_proxy.cc
+++ b/cc/thread_proxy.cc
@@ -977,4 +977,23 @@ ThreadProxy::BeginFrameAndCommitState::~BeginFrameAndCommitState()
 {
 }
 
+bool ThreadProxy::commitPendingForTesting()
+{
+    DCHECK(isMainThread());
+    CommitPendingRequest commitPendingRequest;
+    {
+        DebugScopedSetMainThreadBlocked mainThreadBlocked(this);
+        Proxy::implThread()->postTask(base::Bind(&ThreadProxy::commitPendingOnImplThreadForTesting, base::Unretained(this), &commitPendingRequest));
+        commitPendingRequest.completion.wait();
+    }
+    return commitPendingRequest.commitPending;
+}
+
+void ThreadProxy::commitPendingOnImplThreadForTesting(CommitPendingRequest* request)
+{
+    DCHECK(isImplThread());
+    request->commitPending = m_schedulerOnImplThread->commitPending();
+    request->completion.signal();
+}
+
 }  // namespace cc