Implement quota estimation API from Storage spec

third_party/WebKit/Source/modules/quota/StorageManager.h

 // Copyright 2015 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 StorageManager_h
 #define StorageManager_h
 
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "platform/heap/Heap.h"
 
 namespace blink {
 
 class ScriptPromise;
 class ScriptState;
 
 class StorageManager final : public GarbageCollected<StorageManager>, public ScriptWrappable {
 DEFINE_WRAPPERTYPEINFO();
 public:
     ScriptPromise requestPersistent(ScriptState*);
     ScriptPromise persistentPermission(ScriptState*);
+    ScriptPromise estimate(ScriptState*);
     DECLARE_TRACE();
 };
 
 } // namespace blink
 
 #endif // StorageManager_h