Fix multi-isolate build:

src/platform-win32.cc

Index: src/platform-win32.cc
diff --git a/src/platform-win32.cc b/src/platform-win32.cc
index e23ebe5c387452bc7167b72eaf0acf357521411c..ab03e3d1107bf438dc68b951a2536ec43ec8afab 100644
--- a/src/platform-win32.cc
+++ b/src/platform-win32.cc
@@ -186,13 +186,14 @@ OS::MemCopyFunction CreateMemCopyFunction();
 void OS::MemCopy(void* dest, const void* src, size_t size) {
   if (memcopy_function == NULL) {
     ScopedLock lock(memcopy_function_mutex);
-    Isolate::EnsureDefaultIsolate();
     if (memcopy_function == NULL) {
       OS::MemCopyFunction temp = CreateMemCopyFunction();
       MemoryBarrier();
       memcopy_function = temp;
     }
   }
+  // Note: here we rely on dependent reads being ordered. This is true
+  // on all architectures we currently support.
   (*memcopy_function)(dest, src, size);
 #ifdef DEBUG
   CHECK_EQ(0, memcmp(dest, src, size));
@@ -210,13 +211,14 @@ ModuloFunction CreateModuloFunction();
 double modulo(double x, double y) {
   if (modulo_function == NULL) {
     ScopedLock lock(modulo_function_mutex);
-    Isolate::EnsureDefaultIsolate();
     if (modulo_function == NULL) {
       ModuloFunction temp = CreateModuloFunction();
       MemoryBarrier();
       modulo_function = temp;
     }
   }
+  // Note: here we rely on dependent reads being ordered. This is true
+  // on all architectures we currently support.
   return (*modulo_function)(x, y);
 }
 #else  // Win32