Fix bug in test-macro-assembler-x64 which is the probable cause for hanging on Win64.

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index 46692bc16c1a64a3bae8c69d0e2aff6d0a7c285e..654814c1e6be3403b60d15e00ae7e1f559ae1d6e 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -45,11 +45,11 @@ MacroAssembler::MacroAssembler(void* buffer, int size)
       generating_stub_(false),
       allow_stub_calls_(true),
       root_array_available_(true),
-      code_object_(HEAP->undefined_value()) {
+      code_object_(isolate()->heap()->undefined_value()) {
 }
 
 
-  static intptr_t RootRegisterDelta(ExternalReference other, Isolate* isolate) {
+static intptr_t RootRegisterDelta(ExternalReference other, Isolate* isolate) {
   Address roots_register_value = kRootRegisterBias +
       reinterpret_cast<Address>(isolate->heap()->roots_address());
   intptr_t delta = other.address() - roots_register_value;