Revert of ServiceWorker: Use SimpleCache for the script cache (patchset #7...

Revert of ServiceWorker: Use SimpleCache for the script cache (patchset #7 id:230001 of https://codereview.chromium.org/1140853002/)

Reason for revert:
We'll reland this CL with DiskCache migration code.

Original issue's description:
> ServiceWorker: Use SimpleCache for the script cache
>
> This CL migrates the backend of ServiceWorkerDiskCache from Default to
> SimpleCache on all platforms.
>
> If old DiskCache images exist,
> (1) DiskCache backend fails to open an pre-existing data due to incompatible
> format (in both Default->SimpleCache and SimpleCache->Default cases),
> (2) ServiceWorkerStorage wipes out all cached scripts and registrations via
> DeleteAndStartOver, and
> (3) navigation falls back to network.
>
> BUG=487482
> TEST=manual (use DiskCache and SimpleCache alternately and make sure the system can recover)
>
> Committed: https://crrev.com/a00e5be5a06e626de1b62cbfc7c350bef08647ea
> Cr-Commit-Position: refs/heads/master@{#330274}

TBR=michaeln@chromium.org
BUG=487482

Review URL: https://codereview.chromium.org/1142193002

Cr-Commit-Position: refs/heads/master@{#330505}

content/browser/appcache/appcache_disk_cache.cc

@@ -198,12 +198,8 @@ class AppCacheDiskCache::ActiveCall
 };
 
 AppCacheDiskCache::AppCacheDiskCache()
-#if defined(APPCACHE_USE_SIMPLE_CACHE)
-    : AppCacheDiskCache(true)
-#else
-    : AppCacheDiskCache(false)
-#endif
-{
+    : is_disabled_(false),
+      weak_factory_(this) {
 }
 
 AppCacheDiskCache::~AppCacheDiskCache() {
@@ -308,12 +304,6 @@ int AppCacheDiskCache::DoomEntry(int64 key,
   return ActiveCall::DoomEntry(weak_factory_.GetWeakPtr(), key, callback);
 }
 
-AppCacheDiskCache::AppCacheDiskCache(bool use_simple_cache)
-    : use_simple_cache_(use_simple_cache),
-      is_disabled_(false),
-      weak_factory_(this) {
-}
-
 AppCacheDiskCache::PendingCall::PendingCall()
     : call_type(CREATE),
       key(0),
@@ -343,10 +333,14 @@ int AppCacheDiskCache::Init(
   is_disabled_ = false;
   create_backend_callback_ = new CreateBackendCallbackShim(this);
 
+#if defined(APPCACHE_USE_SIMPLE_CACHE)
+  const net::BackendType backend_type = net::CACHE_BACKEND_SIMPLE;
+#else
+  const net::BackendType backend_type = net::CACHE_BACKEND_DEFAULT;
+#endif
   int rv = disk_cache::CreateCacheBackend(
       cache_type,
-      use_simple_cache_ ? net::CACHE_BACKEND_SIMPLE
-                        : net::CACHE_BACKEND_DEFAULT,
+      backend_type,
       cache_directory,
       cache_size,
       force,

content/browser/appcache/appcache_disk_cache.h

@@ -52,9 +52,6 @@ class CONTENT_EXPORT AppCacheDiskCache
                 const net::CompletionCallback& callback) override;
   int DoomEntry(int64 key, const net::CompletionCallback& callback) override;
 
- protected:
-  explicit AppCacheDiskCache(bool use_simple_cache);
-
  private:
   class CreateBackendCallbackShim;
   class EntryImpl;
@@ -102,7 +99,6 @@ class CONTENT_EXPORT AppCacheDiskCache
   void AddOpenEntry(EntryImpl* entry) { open_entries_.insert(entry); }
   void RemoveOpenEntry(EntryImpl* entry) { open_entries_.erase(entry); }
 
-  bool use_simple_cache_;
   bool is_disabled_;
   net::CompletionCallback init_callback_;
   scoped_refptr<CreateBackendCallbackShim> create_backend_callback_;

content/browser/service_worker/service_worker_disk_cache.cc

@@ -6,10 +6,6 @@
 
 namespace content {
 
-ServiceWorkerDiskCache::ServiceWorkerDiskCache()
-    : AppCacheDiskCache(true /* use_simple_cache */) {
-}
-
 ServiceWorkerResponseReader::ServiceWorkerResponseReader(
     int64 response_id, ServiceWorkerDiskCache* disk_cache)
     : AppCacheResponseReader(response_id, 0, disk_cache) {

content/browser/service_worker/service_worker_disk_cache.h

@@ -18,8 +18,6 @@ namespace content {
 
 class CONTENT_EXPORT ServiceWorkerDiskCache
     : public AppCacheDiskCache {
- public:
-  ServiceWorkerDiskCache();
 };
 
 class CONTENT_EXPORT ServiceWorkerResponseReader