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..72ca341711eaca61ea235af0d03483334de9c892 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 +20,33 @@ 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),
+                      MOJO_MAP_BUFFER_FLAG_NONE);
+  if (result != MOJO_RESULT_OK) {
+    LOG(ERROR) << "Couldn't map buffer for blob ID: " << id;
+    DLOG(FATAL) << "Exiting.";
+    return;
+  }
+  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));
+  result = mojo::UnmapBuffer(blob_buf);
+  if (result != MOJO_RESULT_OK) {
+    LOG(ERROR) << "Couldn't unmap buffer for blob ID: " << id;

[maniscalco, 2016/06/06 15:43:56]

Assuming mojo differentiates between different types of failure (e.g. permission
denied, too many open files), consider logging the error result.  That way, when
we see map/unmap failures we can more easily figure out the cause.

[Kevin M, 2016/06/09 00:08:32]

Done.

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