Factor out the code to write control frame headers into a new constructor of SpdyFrameBuilder.

net/spdy/spdy_frame_builder.cc

Index: net/spdy/spdy_frame_builder.cc
diff --git a/net/spdy/spdy_frame_builder.cc b/net/spdy/spdy_frame_builder.cc
index a7a291e491801d3224c4adf4b4e07f7b20d87b40..1ff94f2d8bfb4637bafa34d644402642f42f5138 100644
--- a/net/spdy/spdy_frame_builder.cc
+++ b/net/spdy/spdy_frame_builder.cc
@@ -9,10 +9,49 @@
 
 namespace net {
 
-SpdyFrameBuilder::SpdyFrameBuilder(size_t size)
+namespace {
+
+// Creates a FlagsAndLength.
+FlagsAndLength CreateFlagsAndLength(SpdyControlFlags flags, size_t length) {
+  DCHECK_EQ(0u, length & ~static_cast<size_t>(kLengthMask));
+  FlagsAndLength flags_length;
+  flags_length.length_ = htonl(static_cast<uint32>(length));
+  DCHECK_EQ(0, flags & ~kControlFlagsMask);
+  flags_length.flags_[0] = flags;
+  return flags_length;
+}
+
+}  // namespace
+
+SpdyFrameBuilder::SpdyFrameBuilder(SpdyControlType type,
+                                   SpdyControlFlags flags,
+                                   int spdy_version,
+                                   size_t size)
+    : buffer_(new char[size]),
+      capacity_(size),
+      length_(0) {
+  FlagsAndLength flags_length = CreateFlagsAndLength(
+      flags, size - SpdyFrame::kHeaderSize);
+  WriteUInt16(kControlFlagMask | spdy_version);
+  WriteUInt16(type);
+  WriteBytes(&flags_length, sizeof(flags_length));
+}
+
+SpdyFrameBuilder::SpdyFrameBuilder(SpdyStreamId stream_id,
+                                   SpdyDataFlags flags,
+                                   size_t size)
     : buffer_(new char[size]),
       capacity_(size),
       length_(0) {
+  DCHECK_EQ(0u, stream_id & ~kStreamIdMask);
+  WriteUInt32(stream_id);
+  size_t length = size - SpdyFrame::kHeaderSize;
+  DCHECK_EQ(0u, length & ~static_cast<size_t>(kLengthMask));
+  FlagsAndLength flags_length;
+  flags_length.length_ = htonl(length);
+  DCHECK_EQ(0, flags & ~kDataFlagsMask);
+  flags_length.flags_[0] = flags;
+  WriteBytes(&flags_length, sizeof(flags_length));
 }
 
 SpdyFrameBuilder::~SpdyFrameBuilder() {