Don't set QUIC's write alarm if we are connection flow control blocked.

net/quic/quic_connection.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // The entity that handles framing writes for a Quic client or server.
 // Each QuicSession will have a connection associated with it.
 //
 // On the server side, the Dispatcher handles the raw reads, and hands off
 // packets via ProcessUdpPacket for framing and processing.
 //
@@ skipping 75 matching lines @@
 
   // Called when the connection failed to write because the socket was blocked.
   virtual void OnWriteBlocked() = 0;
 
   // Called once a specific QUIC version is agreed by both endpoints.
   virtual void OnSuccessfulVersionNegotiation(const QuicVersion& version) = 0;
 
   // Called when a blocked socket becomes writable.
   virtual void OnCanWrite() = 0;
 
-  // Called to ask if any writes are pending in this visitor. Writes may be
-  // pending because they were write-blocked, congestion-throttled or
-  // yielded to other connections.
-  virtual bool HasPendingWrites() const = 0;
+  // Called to ask if the visitor wants to schedule write resumption as it has
+  // both has pending data to write, and is able to write (e.g. based on flow
+  // control limits).
+  // Writes may be pending because they were write-blocked, congestion-throttled
+  // or yielded to other connections.
+  virtual bool WillingAndAbleToWrite() const = 0;
 
   // Called to ask if any handshake messages are pending in this visitor.
   virtual bool HasPendingHandshake() const = 0;
 
   // Called to ask if any streams are open in this visitor, excluding the
   // reserved crypto and headers stream.
   virtual bool HasOpenDataStreams() const = 0;
 };
 
 // Interface which gets callbacks from the QuicConnection at interesting
@@ skipping 641 matching lines @@
   // If non-empty this contains the set of versions received in a
   // version negotiation packet.
   QuicVersionVector server_supported_versions_;
 
   DISALLOW_COPY_AND_ASSIGN(QuicConnection);
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_QUIC_CONNECTION_H_