Add a SpdyFramer extension API implementation.

net/spdy/spdy_frame_builder.h

Index: net/spdy/spdy_frame_builder.h
diff --git a/net/spdy/spdy_frame_builder.h b/net/spdy/spdy_frame_builder.h
index 2715452d90b702b9c371fb32f5f2027562bca9de..721934fcbed4ae91afd66838326f43c2218773f4 100644
--- a/net/spdy/spdy_frame_builder.h
+++ b/net/spdy/spdy_frame_builder.h
@@ -54,14 +54,22 @@ class NET_EXPORT_PRIVATE SpdyFrameBuilder {
                      uint8_t flags,
                      SpdyStreamId stream_id);
 
-  // Populates this frame with a HTTP2 frame prefix with length information.
-  // The given type must be a control frame type.

[Bence, 2017/04/05 13:43:09]

This is incorrect: "control frame" means defined frame type other than HEADERS,
but in fact this method is also used for HEADER frames.

+  // Populates this frame with a HTTP2 frame prefix with type and length
+  // information.  |type| must be a defined type.
   bool BeginNewFrame(const SpdyFramer& framer,
                      SpdyFrameType type,
                      uint8_t flags,
                      SpdyStreamId stream_id,
                      size_t length);
 
+  // Populates this frame with a HTTP2 frame prefix with type and length
+  // information.  |raw_frame_type| must not be a defined frame type.
+  bool BeginNewExtensionFrame(const SpdyFramer& framer,
+                              uint8_t raw_frame_type,
+                              uint8_t flags,
+                              SpdyStreamId stream_id,
+                              size_t length);
+
   // Takes the buffer from the SpdyFrameBuilder.
   SpdySerializedFrame take() {
     SPDY_BUG_IF(output_ != nullptr) << "ZeroCopyOutputBuffer is used to build "
@@ -115,6 +123,14 @@ class NET_EXPORT_PRIVATE SpdyFrameBuilder {
   FRIEND_TEST_ALL_PREFIXES(SpdyFrameBuilderTest, GetWritableOutput);
   FRIEND_TEST_ALL_PREFIXES(SpdyFrameBuilderTest, GetWritableOutputNegative);
 
+  // Populates this frame with a HTTP2 frame prefix with type and length
+  // information.
+  bool BeginNewFrameInternal(const SpdyFramer& framer,
+                             uint8_t raw_frame_type,
+                             uint8_t flags,
+                             SpdyStreamId stream_id,
+                             size_t length);
+
   // Returns a writeable buffer of given size in bytes, to be appended to the
   // currently written frame. Does bounds checking on length but does not
   // increment the underlying iterator. To do so, consumers should subsequently