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..8a0246c9df859100a36a2e174e375ee09b97c61d 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 +20,23 @@ 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.
+  if (!data.is_valid()) {
+    LOG(ERROR) << "Invalid data handle received from renderer process.";

[Wez, 2016/07/01 01:06:56]

Not for this CL: We should work out how in general to turn these sorts of
failures into renderer teardowns, since they indicate the renderer violating the
protocol.

[Kevin M, 2016/07/18 16:35:16]

Filed crbug.com/629096

+    return;
+  }
+
+  if (size > kMaxBlobSizeBytes) {
+    LOG(ERROR) << "Blob size too big: " << size;
+    return;
+  }
+
+  scoped_refptr<BlobData> new_blob(new BlobData);
+  auto mapping = data->Map(size);

[Wez, 2016/07/01 01:06:56]

nit: Don't use auto here, since it's not obvious to the reader what the
resulting type will be without looking up the Map() API, and the explicit type
name won't make the code too verbose.

[dcheng, 2016/07/01 02:04:28]

I missed this, but we need to check that the Map() call succeeds (it will return
nullptr on failure)

[Kevin M, 2016/07/18 16:35:16]

Done.

[Kevin M, 2016/07/18 16:35:16]

Done.

+  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) {