[BlobAsync] Faster shortcuttin, make renderer controller leaky & alive.

storage/browser/blob/blob_async_builder_host.cc

Index: storage/browser/blob/blob_async_builder_host.cc
diff --git a/storage/browser/blob/blob_async_builder_host.cc b/storage/browser/blob/blob_async_builder_host.cc
index 3091604804d33d963604d3ca5282bee112325885..0138de7e7260cf8ea7feb7eb0dbf993bd3c1c768 100644
--- a/storage/browser/blob/blob_async_builder_host.cc
+++ b/storage/browser/blob/blob_async_builder_host.cc
@@ -96,9 +96,7 @@ BlobTransportResult BlobAsyncBuilderHost::StartBuildingBlob(
     BlobStorageContext* context,
     const RequestMemoryCallback& request_memory) {
   DCHECK(context);
-  if (async_blob_map_.find(uuid) == async_blob_map_.end()) {
-    return BlobTransportResult::BAD_IPC;
-  }
+  DCHECK(async_blob_map_.find(uuid) != async_blob_map_.end());
 
   // Step 1: Get the sizes.
   size_t shortcut_memory_size_bytes = 0;