[tracing] Send unique tracing process id for cross-process memory dumps identification.

base/trace_event/memory_dump_manager.cc

 // 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.
 
 #include "base/trace_event/memory_dump_manager.h"
 
 #include <algorithm>
 
 #include "base/atomic_sequence_num.h"
 #include "base/compiler_specific.h"
@@ skipping 139 matching lines @@
 // static
 void MemoryDumpManager::SetInstanceForTesting(MemoryDumpManager* instance) {
   if (instance)
     instance->skip_core_dumpers_auto_registration_for_testing_ = true;
   g_instance_for_testing = instance;
 }
 
 MemoryDumpManager::MemoryDumpManager()
     : delegate_(nullptr),
       memory_tracing_enabled_(0),
+      tracing_process_id_(kInvalidTracingProcessId),
       skip_core_dumpers_auto_registration_for_testing_(false) {
   g_next_guid.GetNext();  // Make sure that first guid is not zero.
 }
 
 MemoryDumpManager::~MemoryDumpManager() {
   base::trace_event::TraceLog::GetInstance()->RemoveEnabledStateObserver(this);
 }
 
 void MemoryDumpManager::Initialize() {
   TRACE_EVENT0(kTraceCategory, "init");  // Add to trace-viewer category list.
@@ skipping 255 matching lines @@
   }
 }
 
 void MemoryDumpManager::OnTraceLogDisabled() {
   AutoLock lock(lock_);
   periodic_dump_timer_.Stop();
   subtle::NoBarrier_Store(&memory_tracing_enabled_, 0);
   session_state_ = nullptr;
 }
 
+// static
+int MemoryDumpManager::ChildProcessIdToTracingProcessId(int child_process_id) {
+  return 1000 + child_process_id;

[picksi, 2015/06/24 11:12:43]

Can we use a named const to explain the 1000, e.g. 'kPreventIDAliasingOffset'
... or whatever it is.

[jam, 2015/06/24 16:38:15]

why is this guessable? i.e. why not a hash?

[Primiano Tucci (use gerrit), 2015/06/24 17:47:34]

+1

+}
+
 MemoryDumpManager::MemoryDumpProviderInfo::MemoryDumpProviderInfo(
     const scoped_refptr<SingleThreadTaskRunner>& task_runner)
     : task_runner(task_runner), consecutive_failures(0), disabled(false) {
 }
 MemoryDumpManager::MemoryDumpProviderInfo::~MemoryDumpProviderInfo() {
 }
 
 }  // namespace trace_event
 }  // namespace base