Move libplatform files into v8::platform namespace

src/libplatform/worker-thread.cc

Index: src/libplatform/worker-thread.cc
diff --git a/src/libplatform/worker-thread.cc b/src/libplatform/worker-thread.cc
index 6b3892cbd2fd62cb82e130bb3debe93fe21285e3..239403b097769d8e75777951f320d84be1937b58 100644
--- a/src/libplatform/worker-thread.cc
+++ b/src/libplatform/worker-thread.cc
@@ -8,7 +8,7 @@
 #include "src/libplatform/task-queue.h"
 
 namespace v8 {
-namespace internal {
+namespace platform {
 
 WorkerThread::WorkerThread(TaskQueue* queue)
     : Thread("V8 WorkerThread"), queue_(queue) {
@@ -28,4 +28,4 @@ void WorkerThread::Run() {
   }
 }
 
-} }  // namespace v8::internal
+} }  // namespace v8::platform