Throttle HttpStreamFactoryImpl::Job to HTTP/2-supported servers

net/spdy/chromium/spdy_session_pool.cc

Index: net/spdy/chromium/spdy_session_pool.cc
diff --git a/net/spdy/chromium/spdy_session_pool.cc b/net/spdy/chromium/spdy_session_pool.cc
index 5b10bf84392987f7351182029a461021b49b7003..f46b4401354f1e526b14a8a62de9b23660bbf87e 100644
--- a/net/spdy/chromium/spdy_session_pool.cc
+++ b/net/spdy/chromium/spdy_session_pool.cc
@@ -439,6 +439,29 @@ void SpdySessionPool::OnNewSpdySessionReady(
   // TODO(mbelshe): Alert other valid requests.
 }
 
+bool SpdySessionPool::StartRequest(const SpdySessionKey& spdy_session_key,
+                                   const base::Closure& callback) {
+  auto iter = spdy_session_pending_request_map_.find(spdy_session_key);
+  if (iter == spdy_session_pending_request_map_.end()) {
+    spdy_session_pending_request_map_.emplace(spdy_session_key,
+                                              std::list<base::Closure>{});
+    return true;
+  }
+  iter->second.push_back(callback);
+  return false;
+}
+
+void SpdySessionPool::ResumeAllPendingRequests(
+    const SpdySessionKey& spdy_session_key) {
+  auto iter = spdy_session_pending_request_map_.find(spdy_session_key);
+  if (iter != spdy_session_pending_request_map_.end()) {
+    for (auto callback : iter->second) {
+      base::ThreadTaskRunnerHandle::Get()->PostTask(FROM_HERE, callback);
+    }
+    spdy_session_pending_request_map_.erase(iter);
+  }
+}
+
 void SpdySessionPool::AddRequestToSpdySessionRequestMap(
     const SpdySessionKey& spdy_session_key,
     HttpStreamFactoryImpl::Request* request) {
@@ -463,6 +486,9 @@ void SpdySessionPool::RemoveRequestFromSpdySessionRequestMap(
   if (request_set.empty())
     spdy_session_request_map_.erase(spdy_session_key);
   request->ResetSpdySessionKey();
+  // If the request failed or canceled, open the floodgate to resume all
+  // requests.
+  ResumeAllPendingRequests(spdy_session_key);

[xunjieli, 2017/06/13 15:23:11]

I remove ResumeNextPendingRequest() to make the logic simpler and easier to
refactor later.

For any failed or canceled Request, RemoveRequestFromSpdySessionRequestMap()
will be called. When that is called, we just open the floodgate to allow
throttled Jobs to go through (rather than the first one in the previous patch). 

For preconnects, since they do not have a Request object, we open the floodgate
when Job::RunLoop() completes. 

 }
 
 void SpdySessionPool::DumpMemoryStats(