Implement CachedMetadata handling on MojoAsyncResourceHandler

content/browser/loader/mojo_async_resource_handler.cc

Index: content/browser/loader/mojo_async_resource_handler.cc
diff --git a/content/browser/loader/mojo_async_resource_handler.cc b/content/browser/loader/mojo_async_resource_handler.cc
index 0d103654468e3923424646aa51031246b07daeef..70fa94a7387857a683bfcd544ed4aaea9ed7ce0d 100644
--- a/content/browser/loader/mojo_async_resource_handler.cc
+++ b/content/browser/loader/mojo_async_resource_handler.cc
@@ -181,6 +181,14 @@ bool MojoAsyncResourceHandler::OnResponseStarted(ResourceResponse* response,
 
   url_loader_client_->OnReceiveResponse(response->head,
                                         std::move(downloaded_file_ptr));
+
+  net::IOBufferWithSize* metadata = GetResponseMetadata(request());
+  if (metadata) {
+    const uint8_t* ptr = reinterpret_cast<const uint8_t*>(metadata->data());

[mmenke, 2017/01/17 18:39:57]

nit:  Maybe ptr -> data?  data isn't exactly a detailed description, but "ptr"
seems even worse.

[yhirano, 2017/01/18 06:22:42]

Done.

+
+    url_loader_client_->OnReceiveCachedMetadata(
+        std::vector<uint8_t>(ptr, ptr + metadata->size()));

[mmenke, 2017/01/13 15:55:04]

Not sure how big this tends to be, but can we somehow avoid a double-copy here? 
(Once to the vector, once to the IPC buffer)

[dcheng, 2017/01/14 11:30:17]

This could be an interesting Mojo feature request. Mojo has something called
CArray (roughly analogous to StringPiece), but usually that's used in
StructTraits. So I suspect that if we were to wrap this in a struct with
typemapping, we would be able to remove a copy... but it would be nice not to
have to do that.

[yhirano, 2017/01/16 05:40:41]

How about adding net::IOBufferWithSize support to IPC?

[mmenke, 2017/01/17 18:39:57]

It's a weird enough type that I don't think that's a great idea (What if we have
another net::IOBuffer subtype and a length, for instance?).  Some general way to
send an array + length as a vector without a copy seems like it would be better,
to me.

[yhirano, 2017/01/18 06:22:42]

OK, let's leave it be. We'll be able to remove the copy when migrating
parameters. Note that we have this copy in AsyncResourceHandler too.

+  }

[mmenke, 2017/01/17 18:40:52]

Also, include <vector> (Same probably goes for both test cc files as well.

[yhirano, 2017/01/18 06:22:42]

Done.

   return true;
 }
 
@@ -323,6 +331,11 @@ MojoResult MojoAsyncResourceHandler::EndWrite(uint32_t written) {
   return mojo::EndWriteDataRaw(shared_writer_->writer(), written);
 }
 
+net::IOBufferWithSize* MojoAsyncResourceHandler::GetResponseMetadata(
+    net::URLRequest* request) {
+  return request->response_info().metadata.get();
+}
+
 void MojoAsyncResourceHandler::OnResponseCompleted(
     const net::URLRequestStatus& status,
     bool* defer) {