Create new versions of SerializeXXX() functions that uses pre-allocated buffer in 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 ee9d36c9f73d5c56cf59dbec073824b659d4e397..1f82dd9d97f2500586d5cdc861e8544644fb936c 100644
--- a/net/spdy/spdy_frame_builder.cc
+++ b/net/spdy/spdy_frame_builder.cc
@@ -80,11 +80,42 @@ bool SpdyFrameBuilder::BeginNewFrame(const SpdyFramer& framer,
   offset_ += length_;
   length_ = 0;
 
+  // TODO(yasong): remove after OverwriteLength() is deleted.
+  bool length_written = false;
+  // Remember where the length field is written. Used for OverwriteLength().
+  if (output_ != nullptr && CanWrite(kLengthFieldLength)) {
+    // Can write the length field.
+    char* dest = nullptr;
+    // |size| is the available bytes in the current memory block.
+    int size = 0;
+    output_->Next(&dest, &size);
+    start_of_current_frame_ = dest;
+    bytes_of_length_written_in_first_block_ =
+        size > (int)kLengthFieldLength ? kLengthFieldLength : size;
+    // If the current block is not enough for the length field, write the
+    // length field here, and remember the pointer to the next block.
+    if (size < (int)kLengthFieldLength) {
+      // Write the first portion of the length field.
+      int value = base::HostToNet32(capacity_ - offset_ - kFrameHeaderSize);
+      memcpy(dest, reinterpret_cast<char*>(&value) + 1, size);
+      Seek(size);
+      output_->Next(&dest, &size);
+      start_of_current_frame_in_next_block_ = dest;
+      int size_left =
+          kLengthFieldLength - bytes_of_length_written_in_first_block_;
+      memcpy(dest, reinterpret_cast<char*>(&value) + 1 + size, size_left);
+      Seek(size_left);
+      length_written = true;
+    }
+  }
+
   // Assume all remaining capacity will be used for this frame. If not,
   // the length will get overwritten when we begin the next frame.
   // Don't check for length limits here because this may be larger than the
   // actual frame length.
-  success &= WriteUInt24(capacity_ - offset_ - kFrameHeaderSize);
+  if (!length_written) {
+    success &= WriteUInt24(capacity_ - offset_ - kFrameHeaderSize);
+  }
   success &= WriteUInt8(type);
   success &= WriteUInt8(flags);
   success &= WriteUInt32(stream_id);
@@ -169,6 +200,30 @@ bool SpdyFrameBuilder::WriteBytes(const void* data, uint32_t data_len) {
 
 bool SpdyFrameBuilder::OverwriteLength(const SpdyFramer& framer,
                                        size_t length) {
+  if (output_ != nullptr) {
+    size_t value = base::HostToNet32(length);
+    if (start_of_current_frame_ != nullptr &&
+        bytes_of_length_written_in_first_block_ == kLengthFieldLength) {
+      // Length field of the current frame is within one memory block.
+      memcpy(start_of_current_frame_, reinterpret_cast<char*>(&value) + 1,
+             kLengthFieldLength);
+      return true;
+    } else if (start_of_current_frame_ != nullptr &&
+               start_of_current_frame_in_next_block_ != nullptr &&
+               bytes_of_length_written_in_first_block_ < kLengthFieldLength) {
+      // Length field of the current frame crosses two memory blocks.
+      memcpy(start_of_current_frame_, reinterpret_cast<char*>(&value) + 1,
+             bytes_of_length_written_in_first_block_);
+      memcpy(start_of_current_frame_in_next_block_,
+             reinterpret_cast<char*>(&value) + 1 +
+                 bytes_of_length_written_in_first_block_,
+             kLengthFieldLength - bytes_of_length_written_in_first_block_);
+      return true;
+    } else {
+      return false;
+    }
+  }
+
   DCHECK_GE(framer.GetFrameMaximumSize(), length);
   bool success = false;
   const size_t old_length = length_;