Clean up thread handling in Blimp browser tests.

blimp/net/blob_channel/blob_channel_sender_impl.h

Index: blimp/net/blob_channel/blob_channel_sender_impl.h
diff --git a/blimp/net/blob_channel/blob_channel_sender_impl.h b/blimp/net/blob_channel/blob_channel_sender_impl.h
index 4c0db42c9dc144363641faca45fafb277932c2a5..1747adda5a73954d9a4f2995c6e67eeaa3534d71 100644
--- a/blimp/net/blob_channel/blob_channel_sender_impl.h
+++ b/blimp/net/blob_channel/blob_channel_sender_impl.h
@@ -11,6 +11,7 @@
 #include <vector>
 
 #include "base/macros.h"
+#include "base/memory/weak_ptr.h"
 #include "base/threading/thread_checker.h"
 #include "blimp/common/blob_cache/blob_cache.h"
 #include "blimp/net/blimp_net_export.h"
@@ -52,6 +53,8 @@ class BLIMP_NET_EXPORT BlobChannelSenderImpl : public BlobChannelSender {
   // delivered, or has been evicted at the receiver.
   std::set<BlobId> receiver_cache_contents_;
 
+  base::WeakPtrFactory<BlobChannelSenderImpl> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(BlobChannelSenderImpl);
 };