workers: Map the current thread-id to the WorkerRunLoop.

Instead of using an AtomicSequenceNumber to find an ID for a worker runloop,
use the ID of the current thread instead.

BUG=none
R=jochen@chromium.org

Review URL: https://codereview.chromium.org/886593002

Cr-Commit-Position: refs/heads/master@{#313786}

content/child/worker_task_runner.cc

@@ -36,9 +36,6 @@ struct WorkerTaskRunner::ThreadLocalState {
 };
 
 WorkerTaskRunner::WorkerTaskRunner() {
-  // Start worker ids at 1, 0 is reserved for the main thread.
-  int id = id_sequence_.GetNext();
-  DCHECK(!id);
 }
 
 bool WorkerTaskRunner::PostTask(
@@ -86,7 +83,8 @@ WorkerTaskRunner::~WorkerTaskRunner() {
 
 void WorkerTaskRunner::OnWorkerRunLoopStarted(const WebWorkerRunLoop& loop) {
   DCHECK(!current_tls_.Get());
-  int id = id_sequence_.GetNext();
+  DCHECK(!base::PlatformThread::CurrentRef().is_null());
+  int id = base::PlatformThread::CurrentId();
   current_tls_.Set(new ThreadLocalState(id));
 
   base::AutoLock locker_(loop_map_lock_);

content/child/worker_task_runner.h

@@ -7,9 +7,9 @@
 
 #include <map>
 
-#include "base/atomic_sequence_num.h"
 #include "base/callback_forward.h"
 #include "base/synchronization/lock.h"
+#include "base/threading/platform_thread.h"
 #include "base/threading/thread_local.h"
 #include "content/common/content_export.h"
 #include "third_party/WebKit/public/platform/WebWorkerRunLoop.h"
@@ -42,14 +42,13 @@ class CONTENT_EXPORT WorkerTaskRunner {
  private:
   friend class WorkerTaskRunnerTest;
 
-  typedef std::map<int, blink::WebWorkerRunLoop> IDToLoopMap;
+  typedef std::map<base::PlatformThreadId, blink::WebWorkerRunLoop> IDToLoopMap;
 
   ~WorkerTaskRunner();
 
   struct ThreadLocalState;
   base::ThreadLocalPointer<ThreadLocalState> current_tls_;
 
-  base::AtomicSequenceNumber id_sequence_;
   IDToLoopMap loop_map_;
   base::Lock loop_map_lock_;
 };