Switch LevelDBWrapper::GetAll to use the new Mojo sync IPC mechanism.

content/renderer/dom_storage/local_storage_cached_area.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_RENDERER_DOM_STORAGE_LOCAL_STORAGE_CACHED_AREA_H_
+#define CONTENT_RENDERER_DOM_STORAGE_LOCAL_STORAGE_CACHED_AREA_H_
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/strings/nullable_string16.h"
+#include "content/common/leveldb_wrapper.mojom.h"
+#include "mojo/public/cpp/bindings/binding.h"
+#include "url/gurl.h"
+#include "url/origin.h"
+
+namespace content {
+class LocalStorageCachedAreas;
+class StoragePartitionService;
+
+// An in-process implementation of LocalStorage using a LevelDB Mojo service.
+// Maintains a complete cache of the origin's Map of key/value pairs for fast
+// access. The cache is primed on first access and changes are written to the
+// backend through the level db interface pointer. Mutations originating in
+// other processes are applied to the cache via LevelDBObserver callbacks.

[michaeln, 2016/03/01 01:38:48]

With modularity in mind, would it make sense for this class to be defined in
components/leveldb? And to be renamed to something more
leveldbwrapperclient'ish.

[jam, 2016/03/01 06:50:54]

it's a bit hard to see since it's still a stub, but this will be local storage
specific. i.e. on mutation events it will call
blink::WebStorageEventDispatcher::dispatchLocalStorageEvent.

indexeddb will do things differently, at least it seems that way so far, but
we'll see when we have other consumers of leveldb whether there's much logic
here to share and we can reconsider then

+class LocalStorageCachedArea : public LevelDBObserver,
+                               public base::RefCounted<LocalStorageCachedArea> {
+ public:
+  LocalStorageCachedArea(const url::Origin& origin,
+                         StoragePartitionService* storage_partition_service,

[michaeln, 2016/03/01 01:38:48]

Questions about unittests? Is it easy to mock out a LevelDBWrapperPtr leveldb_?
Also, with that in mind, would it make sense to pass a LevelDBWrapperPtr into
this ctor instead of the StoragePartitionService*. Have the caller be
responsible for opening the leveldbwrapper for the origin so a unittest could
pass in a mock?

[jam, 2016/03/01 06:50:54]

Re mocking LevelDBWrapperPtr, yep that's easy with mojo (i.e. just have a new
implementation of LevelDBWrapper interface).

Re unittests, yes your suggestion is definitely possible. At this point, it's
not clear if this class will have much logic that makes it worth testing, or
it'll be mostly just pass through calls to LevelDBWrapperPtr. If that's the
case, then the layout tests should be enough IMO.

+                         LocalStorageCachedAreas* cached_areas);
+
+  // These correspond to blink::WebStorageArea.
+  unsigned GetLength();
+  base::NullableString16 GetKey(unsigned index);
+  base::NullableString16 GetItem(const base::string16& key);
+  bool SetItem(const base::string16& key,
+               const base::string16& value,
+               const GURL& page_url);
+  void RemoveItem(const base::string16& key,
+                  const GURL& page_url);
+  void Clear(const GURL& page_url);
+
+  url::Origin origin() { return origin_; }

[michaeln, 2016/03/01 01:38:48]

maybe make this a const ref return value

[jam, 2016/03/01 06:50:54]

Done.

+
+ private:
+  friend class base::RefCounted<LocalStorageCachedArea>;
+  ~LocalStorageCachedArea() override;
+
+  // LevelDBObserver:
+  void KeyChanged(mojo::Array<uint8_t> key,
+                  mojo::Array<uint8_t> new_value,
+                  mojo::Array<uint8_t> old_value,
+                  const mojo::String& source) override;
+  void KeyDeleted(mojo::Array<uint8_t> key,
+                  const mojo::String& source) override;
+  void AllDeleted(const mojo::String& source) override;
+
+  // Synchronously fetches the origin's local storage data if it hasn't been
+  // fetched already.
+  void EnsureLoaded();
+
+  bool loaded_;
+  url::Origin origin_;
+  LevelDBWrapperPtr leveldb_;
+  mojo::Binding<LevelDBObserver> binding_;
+  LocalStorageCachedAreas* cached_areas_;
+
+  DISALLOW_COPY_AND_ASSIGN(LocalStorageCachedArea);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_DOM_STORAGE_LOCAL_STORAGE_CACHED_AREA_H_