Remove a bunch of DeepCopy() calls in the chrome.storage API.

chrome/browser/extensions/api/storage/syncable_settings_storage.h

 // Copyright (c) 2012 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 CHROME_BROWSER_EXTENSIONS_API_STORAGE_SYNCABLE_SETTINGS_STORAGE_H_
 #define CHROME_BROWSER_EXTENSIONS_API_STORAGE_SYNCABLE_SETTINGS_STORAGE_H_
 
 #include "base/compiler_specific.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 37 matching lines @@
   WriteResult Remove(const std::string& key) override;
   WriteResult Remove(const std::vector<std::string>& keys) override;
   WriteResult Clear() override;
   bool Restore() override;
   bool RestoreKey(const std::string& key) override;
 
   // Sync-related methods, analogous to those on SyncableService (handled by
   // ExtensionSettings), but with looser guarantees about when the methods
   // can be called.
 
-  // Must only be called if sync isn't already active.
+  // Starts syncing this storage area. Must only be called if sync isn't
+  // already active.
+  // |sync_state| is the current state of the extension settings in sync.
+  // |sync_processor| is used to write out any changes.
+  // Returns any error when trying to sync, or an empty error on success.
   syncer::SyncError StartSyncing(
-      const base::DictionaryValue& sync_state,
+      scoped_ptr<base::DictionaryValue> sync_state,
       scoped_ptr<SettingsSyncProcessor> sync_processor);
 
-  // May be called at any time (idempotent).
+  // Stops syncing this storage area. May be called at any time (idempotent).
   void StopSyncing();
 
-  // May be called at any time; changes will be ignored if sync isn't active.
-  syncer::SyncError ProcessSyncChanges(const SettingSyncDataList& sync_changes);
+  // Pushes a list of sync changes into this storage area. May be called at
+  // any time, changes will be ignored if sync isn't active.
+  // |sync_changes| are the changes to push.
+  // Returns any error when trying to sync, or an empty error on success.
+  syncer::SyncError ProcessSyncChanges(
+      scoped_ptr<SettingSyncDataList> sync_changes);
 
  private:
   // Sends the changes from |result| to sync if it's enabled.
   void SyncResultIfEnabled(const ValueStore::WriteResult& result);
 
-  // Sends all local settings to sync (synced settings assumed to be empty).
+  // Sends all local settings to sync. This assumes that there are no settings
+  // in sync yet.
+  // |local_state| the local storage state.

[Devlin, 2015/05/15 21:59:08]

nitty nit: missing an is, here.  That said, I don't think this line really adds
much, and this isn't closure compiler (so you don't need to comment on each
parameter).

[not at google - send to devlin, 2015/05/15 23:28:30]

well, sometimes comments on parameters are good, regardless if they happen to go
through a compiler. but I agree in this case it's not that useful (they were
actually from before I decided to rename the parameters).

+  // Returns any error when trying to sync, or an empty error on success.
   syncer::SyncError SendLocalSettingsToSync(
-      const base::DictionaryValue& settings);
+      scoped_ptr<base::DictionaryValue> local_state);
 
   // Overwrites local state with sync state.
+  // |local_state| the local storage state. Will be overwritten by |sync_state|.

[Devlin, 2015/05/15 21:59:08]

nit: Also missing "is"s here (|local_state| _is_...).  These are also in the
opposite order that they appear in the parameter list (I only mention because
they have the same type, so getting them mixed up in a call is easier).

[not at google - send to devlin, 2015/05/15 23:28:30]

Done.

+  // |sync_state| the storage state from sync. Will write over |local_state|.
+  // Returns any error when trying to sync, or an empty error on success.
   syncer::SyncError OverwriteLocalSettingsWithSync(
-      const base::DictionaryValue& sync_state,
-      const base::DictionaryValue& settings);
+      scoped_ptr<base::DictionaryValue> sync_state,
+      scoped_ptr<base::DictionaryValue> local_state);
 
   // Called when an Add/Update/Remove comes from sync.  Ownership of Value*s
   // are taken.
   syncer::SyncError OnSyncAdd(
       const std::string& key,
       base::Value* new_value,
       ValueStoreChangeList* changes);
   syncer::SyncError OnSyncUpdate(
       const std::string& key,
       base::Value* old_value,
@@ skipping 18 matching lines @@
 
   const syncer::ModelType sync_type_;
   const syncer::SyncableService::StartSyncFlare flare_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncableSettingsStorage);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_STORAGE_SYNCABLE_SETTINGS_STORAGE_H_