Use sockets with unread data if they've never been used before.

net/socket/client_socket_pool_base.h

Index: net/socket/client_socket_pool_base.h
diff --git a/net/socket/client_socket_pool_base.h b/net/socket/client_socket_pool_base.h
index 2c2ddb57abc532e329b2e1a30010a7a0f4e2acec..f73a93bf064aedc1c795335663c2c5160b8904b2 100644
--- a/net/socket/client_socket_pool_base.h
+++ b/net/socket/client_socket_pool_base.h
@@ -338,14 +338,19 @@ class NET_EXPORT_PRIVATE ClientSocketPoolBaseHelper
   struct IdleSocket {
     IdleSocket() : socket(NULL) {}
 
+    // An idle socket can't be reused if it is disconnected or has been used
+    // before and has received data unexpectedly (hence no longer idle).  The
+    // unread data would be mistaken for the beginning of the next response if
+    // we were to reuse the socket for a new request.
+    //
+    // Note that a preconnected socket (one that has never been used before)

[mmenke, 2014/02/25 17:01:53]

Suggest rephrasing this to be "Note that a socket that has never been used
before (like a preconnected socket) with unread data may be resued."  While
preconnects are the primary source, there may be other cases (We normally cancel
connect jobs when requests are cancelled, but there may be other ways to get
such a socket...Maybe if we have a single requests, the initial connect job
takes too long, we start a backup connect job, and the request is cancelled, so
we kill a connect job, but just one of them?  Not positive about that case, but
I think the other phrasing is more future proof).

[davidben, 2014/02/27 16:36:35]

Done.

+    // with unread data may be reused.  This may be, e.g., a SPDY SETTINGS
+    // frame.
+    bool IsReusable() const;
+
     // An idle socket should be removed if it can't be reused, or has been idle
     // for too long. |now| is the current time value (TimeTicks::Now()).
     // |timeout| is the length of time to wait before timing out an idle socket.
-    //
-    // An idle socket can't be reused if it is disconnected or has received
-    // data unexpectedly (hence no longer idle).  The unread data would be
-    // mistaken for the beginning of the next response if we were to reuse the
-    // socket for a new request.
     bool ShouldCleanup(base::TimeTicks now, base::TimeDelta timeout) const;
 
     StreamSocket* socket;