Make assertion scopes thread safe.

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index 06a6506b2216580401c8b666ad6de2499d1bc14a..2ef695160d465beab6c84864aad93e975f25d2d9 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -947,8 +947,7 @@ void LCodeGen::PopulateDeoptimizationData(Handle<Code> code) {
 
   Handle<FixedArray> literals =
       factory()->NewFixedArray(deoptimization_literals_.length(), TENURED);
-  { ALLOW_HANDLE_DEREF(isolate(),
-                       "copying a ZoneList of handles into a FixedArray");
+  { AllowDeferredHandleDereference copy_handles;
     for (int i = 0; i < deoptimization_literals_.length(); i++) {
       literals->set(i, *deoptimization_literals_[i]);
     }
@@ -1920,7 +1919,7 @@ void LCodeGen::DoConstantD(LConstantD* instr) {
 
 void LCodeGen::DoConstantT(LConstantT* instr) {
   Handle<Object> value = instr->value();
-  ALLOW_HANDLE_DEREF(isolate(), "smi check");
+  AllowDeferredHandleDereference smi_check;
   if (value->IsSmi()) {
     __ mov(ToRegister(instr->result()), Operand(value));
   } else {
@@ -5291,7 +5290,7 @@ void LCodeGen::DoCheckInstanceType(LCheckInstanceType* instr) {
 void LCodeGen::DoCheckFunction(LCheckFunction* instr) {
   Register reg = ToRegister(instr->value());
   Handle<JSFunction> target = instr->hydrogen()->target();
-  ALLOW_HANDLE_DEREF(isolate(), "smi check");
+  AllowDeferredHandleDereference smi_check;
   if (isolate()->heap()->InNewSpace(*target)) {
     Register reg = ToRegister(instr->value());
     Handle<JSGlobalPropertyCell> cell =