Clean up thread handling in Blimp browser tests.

blimp/net/blob_channel/blob_channel_sender_impl.cc

Index: blimp/net/blob_channel/blob_channel_sender_impl.cc
diff --git a/blimp/net/blob_channel/blob_channel_sender_impl.cc b/blimp/net/blob_channel/blob_channel_sender_impl.cc
index 7baf09fec2051b24b1dfeb51a53c1a73af44ba5d..0ef76195f87c225303392dd86ecf5a3cbb24704c 100644
--- a/blimp/net/blob_channel/blob_channel_sender_impl.cc
+++ b/blimp/net/blob_channel/blob_channel_sender_impl.cc
@@ -15,13 +15,19 @@ namespace blimp {
 
 BlobChannelSenderImpl::BlobChannelSenderImpl(std::unique_ptr<BlobCache> cache,
                                              std::unique_ptr<Delegate> delegate)
-    : cache_(std::move(cache)), delegate_(std::move(delegate)) {
+    : cache_(std::move(cache)),
+      delegate_(std::move(delegate)),
+      weak_factory_(this) {
   DCHECK(cache_);
   DCHECK(delegate_);
 }
 
 BlobChannelSenderImpl::~BlobChannelSenderImpl() {}
 
+base::WeakPtr<BlobChannelSenderImpl> BlobChannelSenderImpl::GetWeakPtr() {
+  return weak_factory_.GetWeakPtr();
+}
+
 std::vector<BlobChannelSender::CacheStateEntry>
 BlobChannelSenderImpl::GetCachedBlobIds() const {
   const auto cache_state = cache_->GetCachedBlobIds();