Clean up thread handling in Blimp browser tests.

blimp/engine/mojo/blob_channel_service.h

Index: blimp/engine/mojo/blob_channel_service.h
diff --git a/blimp/engine/mojo/blob_channel_service.h b/blimp/engine/mojo/blob_channel_service.h
index a137a0694087e56ab08a372acd940d50c251cd55..1ad7552857aaf39fd6f11c4e2a040c87f95b0ad0 100644
--- a/blimp/engine/mojo/blob_channel_service.h
+++ b/blimp/engine/mojo/blob_channel_service.h
@@ -6,22 +6,30 @@
 #define BLIMP_ENGINE_MOJO_BLOB_CHANNEL_SERVICE_H_
 
 #include <string>
+#include <vector>
 
+#include "base/memory/weak_ptr.h"
+#include "base/threading/thread_checker.h"
 #include "blimp/engine/mojo/blob_channel.mojom.h"
+#include "blimp/net/blob_channel/blob_channel_sender.h"
 #include "mojo/public/cpp/bindings/binding_set.h"
 
 namespace blimp {
-
-class BlobChannelSender;
-
 namespace engine {
 
 // Service for processing BlobChannel requests from the renderer.
-// Runs on the browser process.
+// Caller is responsible for executing all methods on the IO thread.
+// The class may interact with objects on the UI thread by posting tasks to
+// |ui_task_runner_|.
 class BlobChannelService : public mojom::BlobChannel {
  public:
-  // |blob_channel_sender| must outlive the Mojo connection.
-  explicit BlobChannelService(BlobChannelSender* blob_channel_sender);
+  // |blob_channel_sender|: The BlobChannelSender object which will receive
+  // blobs and answer delivery status queries.
+  // |blob_sender_task_runner|: The task runner that will process all
+  // interactions with |blob_channel_sender|.
+  BlobChannelService(
+      base::WeakPtr<BlobChannelSender> blob_channel_sender,
+      scoped_refptr<base::SingleThreadTaskRunner> blob_sender_task_runner);
 
   ~BlobChannelService() override;
 
@@ -30,6 +38,13 @@ class BlobChannelService : public mojom::BlobChannel {
   void BindRequest(mojo::InterfaceRequest<mojom::BlobChannel> request);
 
  private:
+  std::vector<BlobChannelSender::CacheStateEntry> GetCachedBlobIdsOnUiThread();
+
+  // Processes the return value from BlobChannelSender::GetCachedBlobIds().
+  void OnGetCachedBlobsCompleted(
+      const BlobChannelService::GetCachedBlobIdsCallback& response_callback,
+      const std::vector<BlobChannelSender::CacheStateEntry>& ids);
+
   // BlobChannel implementation.
   void GetCachedBlobIds(
       const GetCachedBlobIdsCallback& response_callback) override;
@@ -41,7 +56,14 @@ class BlobChannelService : public mojom::BlobChannel {
   mojo::BindingSet<mojom::BlobChannel> bindings_;
 
   // Sender object which will receive the blobs passed over the Mojo service.
-  BlobChannelSender* blob_channel_sender_;
+  base::WeakPtr<BlobChannelSender> blob_channel_sender_;
+
+  // UI thread TaskRunner.
+  scoped_refptr<base::SingleThreadTaskRunner> blob_sender_task_runner_;
+
+  base::ThreadChecker thread_checker_;
+
+  base::WeakPtrFactory<BlobChannelService> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(BlobChannelService);
 };