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..7d15480d764645c19dde1cff92ea1736d02ee7cc 100644
--- a/blimp/net/blob_channel/blob_channel_sender_impl.cc
+++ b/blimp/net/blob_channel/blob_channel_sender_impl.cc
@@ -15,7 +15,9 @@ 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_);
 }