base: Add blame context

base/trace_event/blame_context.h

Index: base/trace_event/blame_context.h
diff --git a/base/trace_event/blame_context.h b/base/trace_event/blame_context.h
new file mode 100644
index 0000000000000000000000000000000000000000..b036676f62700037d49c01f675ae1fad14c9ed33
--- /dev/null
+++ b/base/trace_event/blame_context.h
@@ -0,0 +1,43 @@
+// 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 BASE_TRACE_EVENT_BLAME_CONTEXT_H_
+#define BASE_TRACE_EVENT_BLAME_CONTEXT_H_
+
+#include <inttypes.h>
+
+#include "base/base_export.h"
+#include "base/macros.h"
+#include "base/trace_event/trace_event.h"
+
+namespace base {
+namespace trace_event {
+
+// A blame context represents a logical unit to which we want to attribute
+// different costs (e.g., CPU, network, or memory usage). An example of a blame
+// context is an <iframe> element on a web page. Different subsystems can
+// "enter" and "leave" blame contexts to indicate that they are doing work which
+// should be accounted against this blame context.
+class BASE_EXPORT BlameContext {
+ public:
+  // Indicate that the current thread is now doing work which should count
+  // against this blame context.
+  virtual void Enter() = 0;
+
+  // Leave and stop doing work for a previously entered blame context. If
+  // another blame context of the same type was entered prior to this one, it
+  // becomes the active blame context for this thread again.
+  virtual void Leave() = 0;
+
+ protected:
+  BlameContext() {}
+  virtual ~BlameContext() {}

[danakj, 2016/03/16 18:29:49]

do you need to define this destructor? making a destructor has side effects,
like it deletes default operators and stuff

(do you need a constructor or DISALLOW_COPY_AND_ASSIGN either for an interface?
those seem like they all belong on a concrete class not an interface)

[Sami, 2016/03/17 12:27:13]

I guess I wouldn't have needed this for the interface. It's now gone but thanks
for the tip anyway.

+
+  DISALLOW_COPY_AND_ASSIGN(BlameContext);
+};
+
+}  // namespace trace_event
+}  // namespace base
+
+#endif  // BASE_TRACE_EVENT_BLAME_CONTEXT_H_