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/components/mus/public/interfaces/window_server_test.mojom b/third_party/WebKit/Source/modules/quota/StorageEstimate.idl
similarity index 56%
copy from components/mus/public/interfaces/window_server_test.mojom
copy to third_party/WebKit/Source/modules/quota/StorageEstimate.idl
index 6e03ab23780153e531b9e1dfe98cfa830d249854..3b38d0197a6b9bc751d729f1dccdfeee3366c33d 100644
--- a/components/mus/public/interfaces/window_server_test.mojom
+++ b/third_party/WebKit/Source/modules/quota/StorageEstimate.idl
@@ -2,8 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-module mus.mojom;
+// https://storage.spec.whatwg.org/#api
 
-interface WindowServerTest {
-  EnsureClientHasDrawnWindow(string client_name) => (bool success);
+dictionary StorageEstimate {
+    unsigned long long usage;
+    unsigned long long quota;
 };