net: Introduce SeekableIOBuffer and clean up HttpStreamParser.

net/base/io_buffer.cc

Index: net/base/io_buffer.cc
diff --git a/net/base/io_buffer.cc b/net/base/io_buffer.cc
index b1c72ceb76cf6b8bc6008cc777d7524cf8a46670..004bf0e524303d1677dbe2826ca8e75953e22d44 100644
--- a/net/base/io_buffer.cc
+++ b/net/base/io_buffer.cc
@@ -83,6 +83,49 @@ DrainableIOBuffer::~DrainableIOBuffer() {
   data_ = NULL;
 }
 
+SeekableIOBuffer::SeekableIOBuffer(int size)
+    : IOBuffer(size),
+      begin_(data_),
+      capacity_(size),
+      size_(0),
+      used_(0) {
+}
+
+void SeekableIOBuffer::DidConsume(int bytes) {
+  SetOffset(used_ + bytes);
+}
+
+int SeekableIOBuffer::BytesRemaining() const {
+  return size_ - used_;
+}
+
+int SeekableIOBuffer::BytesConsumed() const {
+  return used_;
+}
+
+void SeekableIOBuffer::SetOffset(int bytes) {
+  DCHECK_GE(bytes, 0);
+  DCHECK_LE(bytes, size_);
+  used_ = bytes;
+  data_ = begin_ + used_;
+}
+
+void SeekableIOBuffer::DidAppend(int bytes) {
+  DCHECK_GE(size_ + bytes, 0);
+  DCHECK_LE(size_ + bytes, capacity_);
+  size_ += bytes;
+}
+
+void SeekableIOBuffer::Clear() {
+  size_ = 0;
+  SetOffset(0);
+}
+
+SeekableIOBuffer::~SeekableIOBuffer() {
+  // data_ will be deleted in IOBuffer::~IOBuffer().
+  data_ = begin_;
+}
+
 GrowableIOBuffer::GrowableIOBuffer()
     : IOBuffer(),
       capacity_(0),