Add uma stats to help evaluate the impact of changes to the quota allocation logic.

components/leveldb/env_mojo.h

 // 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.
 
 #ifndef COMPONENTS_LEVELDB_ENV_MOJO_H_
 #define COMPONENTS_LEVELDB_ENV_MOJO_H_
 
 #include "components/filesystem/public/interfaces/directory.mojom.h"
 #include "components/leveldb/leveldb_mojo_proxy.h"
 #include "third_party/leveldatabase/env_chromium.h"
@@ skipping 36 matching lines @@
 
   uint64_t NowMicros() override;
   void SleepForMicroseconds(int micros) override;
   void Schedule(void (*function)(void* arg), void* arg) override;
   void StartThread(void (*function)(void* arg), void* arg) override;
 
  private:
   void RecordErrorAt(leveldb_env::MethodID method) const override;
   void RecordOSError(leveldb_env::MethodID method,
                      base::File::Error error) const override;
+  void RecordBytesRead(int amount) const override;
+  void RecordBytesWritten(int amount) const override;
 
   void RecordFileError(leveldb_env::MethodID method,
                        filesystem::mojom::FileError error) const;
 
   scoped_refptr<LevelDBMojoProxy> thread_;
   LevelDBMojoProxy::OpaqueDir* dir_;
 
   DISALLOW_COPY_AND_ASSIGN(MojoEnv);
 };
 
 }  // namespace leveldb
 
 #endif  // COMPONENTS_LEVELDB_ENV_MOJO_H_