Report utility process JS memory in task manager.

content/public/browser/process_resource_usage.h

+// 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.
+
+#ifndef CONTENT_PUBLIC_BROWSER_PROCESS_RESOURCE_USAGE_H_
+#define CONTENT_PUBLIC_BROWSER_PROCESS_RESOURCE_USAGE_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "content/common/content_export.h"
+#include "content/public/common/resource_usage_reporter.mojom.h"
+
+namespace content {
+
+// Provides resource usage information about a child process.

[ncarter (slow), 2015/05/07 20:12:44]

Thanks for adding these comments, they are great.

[Anand Mistry (off Chromium), 2015/05/11 05:41:31]

Acknowledged.

+//
+// This is a wrapper around the ResourceUsageReporter Mojo service that exposes
+// information about resources used by a child process. Currently, this is only
+// V8 memory usage, but could be expanded to include other resources such as web
+// cache. This is intended for status viewers such as the task manager and
+// about://memory-internals.
+//
+// To create:
+// 1. Obtain a ResourceUsageReporter connection using the child process's
+//    service registry. i.e:
+//    ResourceUsageReporterPtr service;
+//    process->GetServiceRegistry()->ConnectToRemoteService(&service);
+// 2. If needed, the connection can be passed to another thread using
+//    ResourceUsageReporterPtr::PassInterface().
+// 3. Pass the service to Create().

[ncarter (slow), 2015/05/07 20:12:44]

If you do change the way that the setup dance works in response to the comments
in task_manager, make sure you revisit this comment too.

+//
+// Note: ProcessResourceUsage is thread-hostile and must live on a single
+// thread.
+class CONTENT_EXPORT ProcessResourceUsage {
+ public:
+  virtual ~ProcessResourceUsage() {}
+
+  // Creates a new resource usage reported that is connected to the given Mojo
+  // service. |service| must be bound to the current thread.
+  static scoped_ptr<ProcessResourceUsage> Create(
+      ResourceUsageReporterPtr service);
+
+  // Refresh the resource usage information.
+  virtual void Refresh() = 0;
+
+  // Get V8 memory usage information.
+  virtual bool ReportsV8MemoryStats() const = 0;
+  virtual size_t GetV8MemoryAllocated() const = 0;
+  virtual size_t GetV8MemoryUsed() const = 0;
+};

[ncarter (slow), 2015/05/07 20:12:44]

During my the first pass, I missed the pretty important detail of this being in
content/ 

I hope that it'll be acceptable to move the V8 stats gathering from the chrome
layer into the content layer, but I don't have the best grasp on the rules about
where the boundary is drawn. I expect the content/ OWNERS review to ask for
justification for this (in particular, why it couldn't or shouldn't stay up in
the chrome/ layer, since it was kept there before)

It's probably worth looping jam@ in on this, and you may want to proactively
flesh out an explanation in the CL comment.

[Anand Mistry (off Chromium), 2015/05/11 05:41:31]

I've thought about it and this doesn't belong in content, so I've moved it to
chrome. It simplifies things a little since there's no longer an interface.

+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_BROWSER_PROCESS_RESOURCE_USAGE_H_