Implement quota estimation API from Storage spec

third_party/WebKit/Source/modules/quota/StorageEstimate.idl

Index: third_party/WebKit/Source/modules/quota/StorageEstimate.idl
diff --git a/mash/init/public/interfaces/init.mojom b/third_party/WebKit/Source/modules/quota/StorageEstimate.idl
similarity index 56%
copy from mash/init/public/interfaces/init.mojom
copy to third_party/WebKit/Source/modules/quota/StorageEstimate.idl
index 120d4b8b3351e5ee92d513eadb506a4b9070414e..3b38d0197a6b9bc751d729f1dccdfeee3366c33d 100644
--- a/mash/init/public/interfaces/init.mojom
+++ b/third_party/WebKit/Source/modules/quota/StorageEstimate.idl
@@ -2,9 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-module mash.init.mojom;
+// https://storage.spec.whatwg.org/#api
 
-interface Init {
-  StartService(string name, string user_id);
-  StopServicesForUser(string user_id);
+dictionary StorageEstimate {
+    unsigned long long usage;
+    unsigned long long quota;
 };