Emit session-level WINDOW_UPDATEs less frequently.

net/spdy/spdy_session.cc

Index: net/spdy/spdy_session.cc
diff --git a/net/spdy/spdy_session.cc b/net/spdy/spdy_session.cc
index db791e466b125387d1b4eb028e13d0de20803628..92fc40f42bfa8cdf03198e9d80c0361600d93490 100644
--- a/net/spdy/spdy_session.cc
+++ b/net/spdy/spdy_session.cc
@@ -660,6 +660,7 @@ SpdySession::SpdySession(
                                            : stream_initial_recv_window_size),
       session_send_window_size_(0),
       session_recv_window_size_(0),
+      session_max_recv_window_size_(0),
       session_unacked_recv_window_bytes_(0),
       net_log_(BoundNetLog::Make(net_log, NetLog::SOURCE_HTTP2_SESSION)),
       verify_domain_authentication_(verify_domain_authentication),
@@ -738,6 +739,7 @@ void SpdySession::InitializeWithSocket(
     flow_control_state_ = FLOW_CONTROL_STREAM_AND_SESSION;
     session_send_window_size_ = GetInitialWindowSize(protocol_);
     session_recv_window_size_ = GetInitialWindowSize(protocol_);
+    session_max_recv_window_size_ = GetInitialWindowSize(protocol_);
   } else if (protocol_ >= kProtoSPDY3) {
     flow_control_state_ = FLOW_CONTROL_STREAM;
   } else {
@@ -2793,8 +2795,9 @@ void SpdySession::SendInitialData() {
     // This condition implies that |kDefaultInitialRecvWindowSize| -
     // |session_recv_window_size_| doesn't overflow.
     DCHECK_GT(session_recv_window_size_, 0);
-    IncreaseRecvWindowSize(
-        kDefaultInitialRecvWindowSize - session_recv_window_size_);
+    session_max_recv_window_size_ = kDefaultInitialRecvWindowSize;
+    IncreaseRecvWindowSize(session_max_recv_window_size_ -
+                           session_recv_window_size_);
   }
 
   if (protocol_ <= kProtoSPDY31) {
@@ -3190,8 +3193,7 @@ void SpdySession::IncreaseRecvWindowSize(int32 delta_window_size) {
                                delta_window_size, session_recv_window_size_));
 
   session_unacked_recv_window_bytes_ += delta_window_size;
-  if (session_unacked_recv_window_bytes_ >
-      GetInitialWindowSize(protocol_) / 2) {

[Ryan Hamilton, 2015/04/06 16:27:05]

I'm curious why this didn't work. It *looks* like it should work, but clearly
didn't :>

[Bence, 2015/04/07 12:32:16]

Good question.  So GetInitialWindowSize is 64 kB, while
session_max_recv_window_size_ is 10 MB.  So what this bug means is that every
time the window size goes below 10 MB - 32 kB, a WINDOW_UPDATE is sent to bump
it up to 10 MB.  Instead we only want it when the window size goes below 5 MB. 
Also see bug description.

[Ryan Hamilton, 2015/04/07 14:56:39]

Oh, that method was return the protocol default, not the Chrome initial window
size? Gotcha. I read GetInitialWindowSize and expected that to return 10MB, but
I get it now. Thanks.

+  if (session_unacked_recv_window_bytes_ > session_max_recv_window_size_ / 2) {
     SendWindowUpdateFrame(kSessionFlowControlStreamId,
                           session_unacked_recv_window_bytes_,
                           HIGHEST);