Reland of [Memory UMA] Return the extra_processes_dump map as part of the ResponseCallback

mojo/common/process_id.mojom

Index: mojo/common/process_id.mojom
diff --git a/mojo/common/process_id.mojom b/mojo/common/process_id.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..d72fe6eb96f0940c95494d8c0f7b1777ddc56868
--- /dev/null
+++ b/mojo/common/process_id.mojom
@@ -0,0 +1,12 @@
+// Copyright 2017 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.
+
+module mojo.common.mojom;
+
+struct ProcessId {
+  // This is the storage for the pid, on windows the pid is a DWORD and the
+  // value can be DWORD_MAX which maps gracefully to uint32 while on linux
+  // the pid is a signed int with a max value of 2^22.
+  uint32 pid;
+};