Change the base class of BlameContext into AsyncEnabledStateObserver

base/trace_event/blame_context.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 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/threading/thread_checker.h"
 #include "base/trace_event/trace_log.h"
 
 namespace base {
 namespace trace_event {
 class TracedValue;
 }
 
 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.
 //
 // A blame context can optionally have a parent context, forming a blame context
 // tree. When work is attributed to a particular blame context, it is considered
 // to count against all of that context's children too. This is useful when work
 // cannot be exactly attributed into a more specific context. For example,
 // Javascript garbage collection generally needs to inspect all objects on a
 // page instead looking at each <iframe> individually. In this case the work
 // should be attributed to a blame context which is the parent of all <iframe>
 // blame contexts.
 class BASE_EXPORT BlameContext
-    : public trace_event::TraceLog::EnabledStateObserver {
+    : public trace_event::TraceLog::AsyncEnabledStateObserver {
  public:
   // Construct a blame context belonging to the blame context tree |name|, using
   // the tracing category |category|, identified by |id| from the |scope|
   // namespace. |type| identifies the type of this object snapshot in the blame
   // context tree. |parent_context| is the parent of this blame context or
   // null. Note that all strings must have application lifetime.
   //
   // For example, a blame context which represents a specific <iframe> in a
   // browser frame tree could be specified with:
   //
@@ skipping 21 matching lines @@
                const char* scope,
                int64_t id,
                const BlameContext* parent_context);
   ~BlameContext() override;
 
   // Initialize the blame context, automatically taking a snapshot if tracing is
   // enabled. Must be called before any other methods on this class.
   void Initialize();
 
   // Indicate that the current thread is now doing work which should count
-  // against this blame context.
+  // against this blame context.  This function is allowed to be called in a
+  // thread different from where the blame context was created; However, any
+  // client doing that must be fully responsible for ensuring thready safety.
   void Enter();
 
   // Leave and stop doing work for a previously entered blame context. If
   // another blame context belongin to the same tree was entered prior to this
-  // one, it becomes the active blame context for this thread again.
+  // one, it becomes the active blame context for this thread again.  Similar
+  // to Enter(), this function can be called in a thread different from where
+  // the blame context was created, and the same requirement on thread safety
+  // must be satisfied.
   void Leave();
 
   // Record a snapshot of the blame context. This is normally only needed if a
   // blame context subclass defines custom properties (see AsValueInto) and one
   // or more of those properties have changed.
   void TakeSnapshot();
 
   const char* category() const { return category_; }
   const char* name() const { return name_; }
   const char* type() const { return type_; }
@@ skipping 19 matching lines @@
   const char* name_;
   const char* type_;
   const char* scope_;
   const int64_t id_;
 
   const char* parent_scope_;
   const int64_t parent_id_;
 
   const unsigned char* category_group_enabled_;
 
+  ThreadChecker thread_checker_;
+  WeakPtrFactory<BlameContext> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(BlameContext);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_BLAME_CONTEXT_H_