Remove SpdyDataFrame references from VTL.

Introduces API for creating SPDY DATA frame headers without payload (to avoid extra payload copies).

This lands server change 42554988.

Review URL: https://codereview.chromium.org/12207193

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@183305 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/net/spdy/spdy_frame_builder.h b/net/spdy/spdy_frame_builder.h
index 629bd87..7c52357 100644
--- a/net/spdy/spdy_frame_builder.h
+++ b/net/spdy/spdy_frame_builder.h
@@ -94,6 +94,13 @@
   // with the correct version for the frame being written.
   bool RewriteLength(const SpdyFramer& framer);
 
+  // Update (in-place) the length field in the frame being built to reflect the
+  // given length.
+  // The framer parameter is used to determine version-specific location and
+  // size information of the length field to be written, and must be initialized
+  // with the correct version for the frame being written.
+  bool OverwriteLength(const SpdyFramer& framer, size_t length);
+
  protected:
   const char* end_of_payload() const { return buffer_.get() + length_; }