Add support for ManagedMemoryPolicy (de)serialization

cc/proto/memory_allocation.proto

 // 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.
 
 syntax = "proto2";
 
+package cc.proto;
+
 option optimize_for = LITE_RUNTIME;
 
-package cc.proto;
-
-message SkRegion {
-  enum Op {
-    Op_Difference = 0;
-    Op_Intersect = 1;
-    Op_Union = 2;
-    Op_XOR = 3;
-    Op_ReverseDifference = 4;
-    Op_Replace = 5;
+message MemoryAllocation {
+  enum PriorityCutoff {
+    UNKNOWN = 0;
+    ALLOW_NOTHING = 1;
+    ALLOW_REQUIRED_ONLY = 2;
+    ALLOW_NICE_TO_HAVE = 3;
+    ALLOW_EVERYTHING = 4;
   }
-}
+}