Add helper function for SPDY 4

net/spdy/spdy_framer.cc

Index: net/spdy/spdy_framer.cc
diff --git a/net/spdy/spdy_framer.cc b/net/spdy/spdy_framer.cc
index b8b57c19e3a90e34c4b78bf2e23b7dd8bb37a24e..a6423e157b1e2cd67bc24077fe9001bb0c9104e7 100644
--- a/net/spdy/spdy_framer.cc
+++ b/net/spdy/spdy_framer.cc
@@ -253,6 +253,13 @@ size_t SpdyFramer::GetCredentialMinimumSize() const {
   return GetControlFrameHeaderSize() + 2;
 }
 
+size_t SpdyFramer::GetDataFrameMaximumPayload() const {
+  if (protocol_version() < 4) {
+    return 0xffffff - GetDataFrameMinimumSize();

[Ryan Hamilton, 2013/04/08 16:11:45]

I really think these values should be constants which comments.  For some
reason, hkhalil seems allergic to this appoach, however.

+  }
+  return 0xffff - GetDataFrameMinimumSize();
+}
+
 const char* SpdyFramer::StateToString(int state) {
   switch (state) {
     case SPDY_ERROR: