[TaskManager] Allow a Task to mutate its PID after creation

chrome/browser/task_manager/sampling/task_group.cc

Index: chrome/browser/task_manager/sampling/task_group.cc
diff --git a/chrome/browser/task_manager/sampling/task_group.cc b/chrome/browser/task_manager/sampling/task_group.cc
index ce8460050d72812df030d2c1fdee2f683bb1718a..ba4d286110eb553ff1b74f3e20000e8ae14fd93d 100644
--- a/chrome/browser/task_manager/sampling/task_group.cc
+++ b/chrome/browser/task_manager/sampling/task_group.cc
@@ -108,32 +108,33 @@ TaskGroup::TaskGroup(
       gpu_memory_has_duplicates_(false),
       is_backgrounded_(false),
       weak_ptr_factory_(this) {
-  scoped_refptr<TaskGroupSampler> sampler(
-      new TaskGroupSampler(base::Process::Open(proc_id),
-                           blocking_pool_runner,
-                           base::Bind(&TaskGroup::OnCpuRefreshDone,
-                                      weak_ptr_factory_.GetWeakPtr()),
-                           base::Bind(&TaskGroup::OnMemoryUsageRefreshDone,
-                                      weak_ptr_factory_.GetWeakPtr()),
-                           base::Bind(&TaskGroup::OnIdleWakeupsRefreshDone,
-                                      weak_ptr_factory_.GetWeakPtr()),
+  if (process_id_ != base::kNullProcessId) {
+    worker_thread_sampler_ = base::MakeRefCounted<TaskGroupSampler>(
+        base::Process::Open(process_id_), blocking_pool_runner,
+        base::Bind(&TaskGroup::OnCpuRefreshDone,
+                   weak_ptr_factory_.GetWeakPtr()),
+        base::Bind(&TaskGroup::OnMemoryUsageRefreshDone,
+                   weak_ptr_factory_.GetWeakPtr()),
+        base::Bind(&TaskGroup::OnIdleWakeupsRefreshDone,
+                   weak_ptr_factory_.GetWeakPtr()),
 #if defined(OS_LINUX)
-                           base::Bind(&TaskGroup::OnOpenFdCountRefreshDone,
-                                      weak_ptr_factory_.GetWeakPtr()),
+        base::Bind(&TaskGroup::OnOpenFdCountRefreshDone,
+                   weak_ptr_factory_.GetWeakPtr()),
 #endif  // defined(OS_LINUX)
-                           base::Bind(&TaskGroup::OnProcessPriorityDone,
-                                      weak_ptr_factory_.GetWeakPtr())));
-  worker_thread_sampler_.swap(sampler);
-
-  shared_sampler_->RegisterCallbacks(
-      process_id_, base::Bind(&TaskGroup::OnIdleWakeupsRefreshDone,
-                              weak_ptr_factory_.GetWeakPtr()),
-      base::Bind(&TaskGroup::OnPhysicalMemoryUsageRefreshDone,
-                 weak_ptr_factory_.GetWeakPtr()),
-      base::Bind(&TaskGroup::OnStartTimeRefreshDone,
-                 weak_ptr_factory_.GetWeakPtr()),
-      base::Bind(&TaskGroup::OnCpuTimeRefreshDone,
-                 weak_ptr_factory_.GetWeakPtr()));
+        base::Bind(&TaskGroup::OnProcessPriorityDone,
+                   weak_ptr_factory_.GetWeakPtr()));
+
+    shared_sampler_->RegisterCallbacks(
+        process_id_,
+        base::Bind(&TaskGroup::OnIdleWakeupsRefreshDone,
+                   weak_ptr_factory_.GetWeakPtr()),
+        base::Bind(&TaskGroup::OnPhysicalMemoryUsageRefreshDone,
+                   weak_ptr_factory_.GetWeakPtr()),
+        base::Bind(&TaskGroup::OnStartTimeRefreshDone,
+                   weak_ptr_factory_.GetWeakPtr()),
+        base::Bind(&TaskGroup::OnCpuTimeRefreshDone,
+                   weak_ptr_factory_.GetWeakPtr()));
+  }
 }
 
 TaskGroup::~TaskGroup() {
@@ -223,7 +224,8 @@ void TaskGroup::Refresh(const gpu::VideoMemoryUsageStats& gpu_memory_stats,
   // 9-  Idle Wakeups per second.
   // 10-  (Linux and ChromeOS only) The number of file descriptors current open.
   // 11- Process priority (foreground vs. background).
-  worker_thread_sampler_->Refresh(refresh_flags);
+  if (worker_thread_sampler_)
+    worker_thread_sampler_->Refresh(refresh_flags);
 }
 
 Task* TaskGroup::GetTaskById(TaskId task_id) const {