ServiceWorker: Stop asynchronously creating response accessors to fix crash due to null context

content/browser/service_worker/service_worker_cache_writer.h

Index: content/browser/service_worker/service_worker_cache_writer.h
diff --git a/content/browser/service_worker/service_worker_cache_writer.h b/content/browser/service_worker/service_worker_cache_writer.h
index e4c38ccddfab8264d8e54f59b01c20ebde52305e..7f08708187d3ba8d64a8ed9daa40f5b42c8510e0 100644
--- a/content/browser/service_worker/service_worker_cache_writer.h
+++ b/content/browser/service_worker/service_worker_cache_writer.h
@@ -41,22 +41,13 @@ class CONTENT_EXPORT ServiceWorkerCacheWriter {
  public:
   using OnWriteCompleteCallback = base::Callback<void(net::Error)>;
 
-  // The types for the factory functions passed into the constructor. These are
-  // responsible for creating readers from the existing cache entry and writers
-  // to the new cache entry when called. These are passed in as factories
-  // instead of passing readers and writers in directly to avoid creating
-  // writers to entries that won't be updated, and because this class may need
-  // multiple readers internally.

[nhiroki, 2016/02/18 04:21:53]

Creating unused readers and writers wouldn't cost a lot because their ctors just
set up fields and don't interact with the disk cache. Rather, we could reduce
code complexity by creating the readers and writers synchronously.

[falken, 2016/02/18 04:43:59]

Thanks for this comment, I was wondering why it was originally written this way
and why it's ok to change it (and thanks to the the writer of the original code
comment!).

-  using ResponseReaderCreator =
-      base::Callback<scoped_ptr<ServiceWorkerResponseReader>(void)>;
-  using ResponseWriterCreator =
-      base::Callback<scoped_ptr<ServiceWorkerResponseWriter>(void)>;
-
   // The existing reader may be null, in which case this instance will

[falken, 2016/02/18 04:43:59]

change "existing reader" to |compare_reader|

[nhiroki, 2016/02/18 07:09:48]

Done.

   // unconditionally write back data supplied to |MaybeWriteHeaders| and
   // |MaybeWriteData|.
-  ServiceWorkerCacheWriter(const ResponseReaderCreator& reader_creator,
-                           const ResponseWriterCreator& writer_creator);
+  ServiceWorkerCacheWriter(
+      scoped_ptr<ServiceWorkerResponseReader> compare_reader,
+      scoped_ptr<ServiceWorkerResponseReader> copy_reader,
+      scoped_ptr<ServiceWorkerResponseWriter> writer);
 
   ~ServiceWorkerCacheWriter();
 
@@ -219,8 +210,6 @@ class CONTENT_EXPORT ServiceWorkerCacheWriter {
 
   size_t compare_offset_;
 
-  ResponseReaderCreator reader_creator_;
-  ResponseWriterCreator writer_creator_;
   scoped_ptr<ServiceWorkerResponseReader> compare_reader_;
   scoped_ptr<ServiceWorkerResponseReader> copy_reader_;
   scoped_ptr<ServiceWorkerResponseWriter> writer_;