Use shared memory for moving data over BlobChannel Mojo interface.

blimp/engine/mojo/blob_channel_service.cc

Index: blimp/engine/mojo/blob_channel_service.cc
diff --git a/blimp/engine/mojo/blob_channel_service.cc b/blimp/engine/mojo/blob_channel_service.cc
index 0234df60698b3a2c2628537b7e66cfd9ae44bfd9..34d35ee2ae6e5a2fb2a10129df6d4e0ff827a67d 100644
--- a/blimp/engine/mojo/blob_channel_service.cc
+++ b/blimp/engine/mojo/blob_channel_service.cc
@@ -5,6 +5,7 @@
 #include "blimp/engine/mojo/blob_channel_service.h"
 
 #include "blimp/net/blob_channel/blob_channel_sender.h"
+#include "mojo/public/cpp/system/buffer.h"
 
 namespace blimp {
 namespace engine {
@@ -19,8 +20,14 @@ BlobChannelService::BlobChannelService(BlobChannelSender* blob_channel_sender,
 BlobChannelService::~BlobChannelService() {}
 
 void BlobChannelService::PutBlob(const mojo::String& id,
-                                 const mojo::String& data) {
-  blob_channel_sender_->PutBlob(id, new BlobData(data));
+                                 mojo::ScopedSharedBufferHandle data,
+                                 uint32_t size) {
+  // Map |data| into the address space and copy out its contents.
+  DCHECK(data.is_valid());

[dcheng, 2016/06/25 01:06:31]

The comments imply this is coming from the renderer. I'm a bit fuzzy on the
Blimp process model, but I guess the renderer is still untrusted? So it seems
like this needs to be an if (), not a DCHECK().

[Kevin M, 2016/06/27 17:31:12]

Done.

+  scoped_refptr<BlobData> new_blob(new BlobData);
+  auto mapping = data->Map(size);
+  new_blob->data.assign(reinterpret_cast<const char*>(mapping.get()), size);
+  blob_channel_sender_->PutBlob(id, std::move(new_blob));
 }
 
 void BlobChannelService::DeliverBlob(const mojo::String& id) {