Implement Drain() on HttpPipelinedStream.

net/http/http_response_body_drainer.cc

Index: net/http/http_response_body_drainer.cc
diff --git a/net/http/http_response_body_drainer.cc b/net/http/http_response_body_drainer.cc
index aefb18026528f2b90307349fc153e15cbdd7d3c6..bbd27276b1711dafa2b7f12ba563ff454255fe5e 100644
--- a/net/http/http_response_body_drainer.cc
+++ b/net/http/http_response_body_drainer.cc
@@ -25,7 +25,25 @@ HttpResponseBodyDrainer::HttpResponseBodyDrainer(HttpStream* stream)
 HttpResponseBodyDrainer::~HttpResponseBodyDrainer() {}
 
 void HttpResponseBodyDrainer::Start(HttpNetworkSession* session) {
-  read_buf_ = new IOBuffer(kDrainBodyBufferSize);
+  StartWithSize(session, kDrainBodyBufferSize);
+}
+
+void HttpResponseBodyDrainer::StartWithSize(HttpNetworkSession* session,
+                                            int num_bytes_to_drain) {
+  DCHECK_LE(0, num_bytes_to_drain);
+  // TODO(simonjam): Consider raising this limit if we're pipelining. If we have
+  // a bunch of responses in the pipeline, we should be less willing to give up
+  // while draining.
+  if (num_bytes_to_drain > kDrainBodyBufferSize) {
+    Finish(ERR_RESPONSE_BODY_TOO_BIG_TO_DRAIN);
+    return;
+  } else if (num_bytes_to_drain == 0) {
+    Finish(OK);
+    return;
+  }
+
+  read_size_ = num_bytes_to_drain;
+  read_buf_ = new IOBuffer(read_size_);
   next_state_ = STATE_DRAIN_RESPONSE_BODY;
   int rv = DoLoop(OK);
 
@@ -71,7 +89,7 @@ int HttpResponseBodyDrainer::DoDrainResponseBody() {
   next_state_ = STATE_DRAIN_RESPONSE_BODY_COMPLETE;
 
   return stream_->ReadResponseBody(
-      read_buf_, kDrainBodyBufferSize - total_read_,
+      read_buf_, read_size_ - total_read_,
       &io_callback_);
 }