Add TaskScheduler::InitParams and accept it in TaskSchedulerImpl constructor.

base/task_scheduler/task_scheduler_impl.cc

Index: base/task_scheduler/task_scheduler_impl.cc
diff --git a/base/task_scheduler/task_scheduler_impl.cc b/base/task_scheduler/task_scheduler_impl.cc
index e5c8abf716306f8602b0cde8786e10dc292f1739..64da1b77e045188a07ed1ece0c7504395310db97 100644
--- a/base/task_scheduler/task_scheduler_impl.cc
+++ b/base/task_scheduler/task_scheduler_impl.cc
@@ -24,6 +24,52 @@
 namespace base {
 namespace internal {
 
+namespace {
+
+enum EnvironmentType {
+  BACKGROUND = 0,
+  BACKGROUND_BLOCKING,
+  FOREGROUND,
+  FOREGROUND_BLOCKING,
+  ENVIRONMENT_COUNT  // Always last.
+};
+
+// Order must match the EnvironmentType enum.
+constexpr struct {
+  // The threads and histograms of this environment will be labeled with
+  // task scheduler name + |name_suffix|.

[robliao, 2017/03/23 18:00:52]

Might be clearer to say the name from InitParams + |name_suffix|

[fdoray, 2017/03/24 14:00:38]

We don't use the name from InitParams, we use the |name| argument of
TaskSchedulerImpl::Create() + |name_suffix|.

+  const char* name_suffix;
+
+  // Preferred priority for threads in this environment; the actual thread
+  // priority depends on shutdown state and platform capabilities.
+  ThreadPriority priority_hint;
+
+  // Offset of the SchedulerWorkerPoolParams corresponding to this environement
+  // in TaskSchedulerInitParams.

[robliao, 2017/03/23 18:00:52]

Worth discussing that this allows us to easily use a for loop to get the right
init params.

[fdoray, 2017/03/24 14:00:38]

Done.

+  size_t offset;
+} kEnvironmentParams[] = {
+    {"Background", base::ThreadPriority::BACKGROUND,
+     offsetof(TaskScheduler::InitParams, background_worker_pool_params)},
+    {"BackgroundBlocking", base::ThreadPriority::BACKGROUND,
+     offsetof(TaskScheduler::InitParams,
+              background_blocking_worker_pool_params)},
+    {"Foreground", base::ThreadPriority::NORMAL,
+     offsetof(TaskScheduler::InitParams, foreground_worker_pool_params)},
+    {"ForegroundBlocking", base::ThreadPriority::NORMAL,
+     offsetof(TaskScheduler::InitParams,
+              foreground_blocking_worker_pool_params)},
+};
+
+size_t GetEnvironmentIndexForTraits(const TaskTraits& traits) {
+  const bool is_background =
+      traits.priority() == base::TaskPriority::BACKGROUND;
+  if (traits.may_block() || traits.with_base_sync_primitives())
+    return is_background ? BACKGROUND_BLOCKING : FOREGROUND_BLOCKING;
+  return is_background ? BACKGROUND : FOREGROUND;
+}
+
+}  // namespace
+
 // static
 std::unique_ptr<TaskSchedulerImpl> TaskSchedulerImpl::Create(
     const std::vector<SchedulerWorkerPoolParams>& worker_pool_params_vector,
@@ -35,6 +81,31 @@ std::unique_ptr<TaskSchedulerImpl> TaskSchedulerImpl::Create(
   return scheduler;
 }
 
+// static
+std::unique_ptr<TaskSchedulerImpl> TaskSchedulerImpl::Create(
+    const std::string& name,
+    const TaskScheduler::InitParams& init_params) {
+  // Create a vector of SchedulerWorkerPoolParams using names and priority hints
+  // derived from |kEnvironmentParams| and other params from |init_params|.
+  std::vector<SchedulerWorkerPoolParams> worker_pool_params_vector;
+  for (const auto& environment_params : kEnvironmentParams) {
+    const SchedulerWorkerPoolParams& worker_pool_params_in =
+        *reinterpret_cast<const SchedulerWorkerPoolParams*>(
+            reinterpret_cast<const char*>(&init_params) +

[robliao, 2017/03/23 18:00:52]

Instead of const char*, should this be uintptr_t instead to allow for varying
bitness?

[fdoray, 2017/03/24 14:00:38]

Done.

+            environment_params.offset);
+    worker_pool_params_vector.emplace_back(
+        name + environment_params.name_suffix, environment_params.priority_hint,
+        worker_pool_params_in.standby_thread_policy(),
+        worker_pool_params_in.max_threads(),
+        worker_pool_params_in.suggested_reclaim_time(),
+        worker_pool_params_in.backward_compatibility());
+  }
+  DCHECK_EQ(static_cast<size_t>(ENVIRONMENT_COUNT),
+            worker_pool_params_vector.size());
+
+  return Create(worker_pool_params_vector, Bind(&GetEnvironmentIndexForTraits));
+}
+
 TaskSchedulerImpl::~TaskSchedulerImpl() {
 #if DCHECK_IS_ON()
   DCHECK(join_for_testing_returned_.IsSet());