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..9f535cb2d238572d55686ba92aafe78577563272 100644
--- a/blimp/engine/mojo/blob_channel_service.cc
+++ b/blimp/engine/mojo/blob_channel_service.cc
@@ -19,8 +19,24 @@ 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,
+                                 const PutBlobCallback& callback) {
+  // Map |data| into memory.
+  char* blob_buf = nullptr;
+  MojoResult result =
+      mojo::MapBuffer(data.get(), 0, size, reinterpret_cast<void**>(&blob_buf),

[maniscalco, 2016/06/03 16:43:53]

#include "mojo/public/cpp/system/buffer.h" to get mojo::MapBuffer?

[Kevin M, 2016/06/03 17:14:57]

Done.

+                      MOJO_MAP_BUFFER_FLAG_NONE);
+  DCHECK_EQ(MOJO_RESULT_OK, result);
+  DCHECK(blob_buf);
+
+  scoped_refptr<BlobData> new_blob(new BlobData);
+  new_blob->data.assign(blob_buf, size);
+  blob_channel_sender_->PutBlob(id, std::move(new_blob));
+  mojo::UnmapBuffer(blob_buf);

[maniscalco, 2016/06/03 16:43:53]

Check the result of UnmapBuffer?

[Kevin M, 2016/06/03 17:14:57]

OK. I'm using DCHECK w/return so that we don't blow up the browser process if
the bug is essentially recoverable.

+
+  // Signals the renderer side that we are done with the shared memory |data|.
+  callback.Run();
 }
 
 void BlobChannelService::DeliverBlob(const mojo::String& id) {