Revert of Use TaskScheduler instead of WorkerPool in v8_platform.cc.

gin/v8_platform.cc

Index: gin/v8_platform.cc
diff --git a/gin/v8_platform.cc b/gin/v8_platform.cc
index 9c69aa97721e78c151e9c1e44866586d4e32006a..4fe7c7ceced0d5f4d164ea14c548aca3aba0b1d6 100644
--- a/gin/v8_platform.cc
+++ b/gin/v8_platform.cc
@@ -7,8 +7,7 @@
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/sys_info.h"
-#include "base/task_scheduler/post_task.h"
-#include "base/task_scheduler/task_scheduler.h"
+#include "base/threading/worker_pool.h"
 #include "base/trace_event/trace_event.h"
 #include "gin/per_isolate_data.h"
 
@@ -43,11 +42,6 @@ class IdleTaskWithLocker : public v8::IdleTask {
   DISALLOW_COPY_AND_ASSIGN(IdleTaskWithLocker);
 };
 
-base::TaskTraits GetBackgroundThreadTaskTraits() {
-  return base::TaskTraits().WithShutdownBehavior(
-      base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN);
-}
-
 }  // namespace
 
 // static
@@ -58,16 +52,25 @@ V8Platform::V8Platform() {}
 V8Platform::~V8Platform() {}
 
 size_t V8Platform::NumberOfAvailableBackgroundThreads() {
-  return base::TaskScheduler::GetInstance()
-      ->GetMaxConcurrentTasksWithTraitsDeprecated(
-          GetBackgroundThreadTaskTraits());
+  // WorkerPool will currently always create additional threads for posted
+  // background tasks, unless there are threads sitting idle (on posix).
+  // Indicate that V8 should create no more than the number of cores available,
+  // reserving one core for the main thread.
+  const size_t available_cores =
+    static_cast<size_t>(base::SysInfo::NumberOfProcessors());
+  if (available_cores > 1) {
+    return available_cores - 1;
+  }
+  return 1;
 }
 
 void V8Platform::CallOnBackgroundThread(
     v8::Task* task,
     v8::Platform::ExpectedRuntime expected_runtime) {
-  base::PostTaskWithTraits(FROM_HERE, GetBackgroundThreadTaskTraits(),
-                           base::Bind(&v8::Task::Run, base::Owned(task)));
+  base::WorkerPool::PostTask(
+      FROM_HERE,
+      base::Bind(&v8::Task::Run, base::Owned(task)),
+      expected_runtime == v8::Platform::kLongRunningTask);
 }
 
 void V8Platform::CallOnForegroundThread(v8::Isolate* isolate, v8::Task* task) {