Refactor and cleanup VirtualMemory.

test/cctest/test-code-stubs-x64.cc

Index: test/cctest/test-code-stubs-x64.cc
diff --git a/test/cctest/test-code-stubs-x64.cc b/test/cctest/test-code-stubs-x64.cc
index 4af5b45d7c62135119a37b7825003f538647fd4a..a058118aa7a3b8a60322ea54e7fe775c3566235d 100644
--- a/test/cctest/test-code-stubs-x64.cc
+++ b/test/cctest/test-code-stubs-x64.cc
@@ -46,9 +46,10 @@ ConvertDToIFunc MakeConvertDToIFuncTrampoline(Isolate* isolate,
                                               Register destination_reg) {
   // Allocate an executable page of memory.
   size_t actual_size;
-  byte* buffer = static_cast<byte*>(OS::Allocate(Assembler::kMinimalBufferSize,
-                                                   &actual_size,
-                                                   true));
+  byte* buffer = static_cast<byte*>(VirtualMemory::AllocateRegion(
+          Assembler::kMinimalBufferSize,
+          &actual_size,
+          VirtualMemory::EXECUTABLE));
   CHECK(buffer);
   HandleScope handles(isolate);
   MacroAssembler assm(isolate, buffer, static_cast<int>(actual_size));