cc: Fix cc_unittests when main frame before activation is enabled.

cc/trees/proxy_impl.cc

Index: cc/trees/proxy_impl.cc
diff --git a/cc/trees/proxy_impl.cc b/cc/trees/proxy_impl.cc
index 123e394d508152a4f3a1972ecebefeec55b7555e..92b4506c418a02b51ed4d36467c24b0ff7ec77c5 100644
--- a/cc/trees/proxy_impl.cc
+++ b/cc/trees/proxy_impl.cc
@@ -184,7 +184,6 @@ void ProxyImpl::BeginMainFrameAbortedOnImpl(
                CommitEarlyOutReasonToString(reason));
   DCHECK(IsImplThread());
   DCHECK(scheduler_->CommitPending());
-  DCHECK(!layer_tree_host_impl_->pending_tree());

[enne (OOO), 2016/05/13 01:26:02]

This seems reasonable to me.  If we can send a main frame with the pending tree
existing, I think it's fine to remove this, or move this dcheck to the
scheduler.

[sunnyps, 2016/05/14 00:41:19]

I'm moving this change to https://codereview.chromium.org/1984453003/

 
   if (CommitEarlyOutHandledCommit(reason)) {
     SetInputThrottledUntilCommitOnImpl(false);