AddEngagementBudget and SpendBudget added to BudgetDatabase.

chrome/browser/budget_service/budget.proto

 // 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.
 
 syntax = "proto2";
 
 package budget_service;
 
 // Chrome requires this.
 option optimize_for = LITE_RUNTIME;
 
-// Next available id: 2
+// Next available id: 3
 message Budget {
   // The sequence of budget chunks and their expiration times.
   repeated BudgetChunk budget = 1;
+
+  // The timestamp of the last time that new budget was awarded. This stores
+  // the internal value needed to construct a base::Time object.
+  optional int64 last_updated = 2;

[johnme, 2016/08/19 18:48:35]

Nit: rename this to clarify that only engagement awards update this value; other
budget grants do not.

[harkness, 2016/08/22 13:46:25]

Done.

 }
 
 // Next available id: 3
 message BudgetChunk {
   // The amount of budget remaining in this chunk.
   optional double amount = 1;
 
   // The timestamp when the budget expires. This stores the internal value
   // needed to construct a base::Time object.
   optional int64 expiration = 2;

[johnme, 2016/08/19 18:48:35]

Optional: instead of storing expiration times for each BudgetChunk and a
per-origin last_updated, you could just store grant times for each BudgetChunk.
I'm not sure if that makes things harder or easier.

[harkness, 2016/08/22 13:46:25]

That wouldn't actually work, since even if a site currently has no budget, you
need to keep track of when the next chunk can be awarded.

 }