Remove unnecessary Isolate::Current calls from hydrogen-instructions

BUG=none
R=vogelheim@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/1144523004

Cr-Commit-Position: refs/heads/master@{#28408}

src/hydrogen-instructions.cc

@@ -2976,7 +2976,7 @@ std::ostream& HConstant::PrintDataTo(std::ostream& os) const {  // NOLINT
     os << reinterpret_cast<void*>(external_reference_value_.address()) << " ";
   } else {
     // The handle() method is silently and lazily mutating the object.
-    Handle<Object> h = const_cast<HConstant*>(this)->handle(Isolate::Current());
+    Handle<Object> h = const_cast<HConstant*>(this)->handle(isolate());
     os << Brief(*h) << " ";
     if (HasStableMapValue()) os << "[stable-map] ";
     if (HasObjectMap()) os << "[map " << *ObjectMap().handle() << "] ";

src/hydrogen-instructions.h

@@ -6843,7 +6843,7 @@ class HStoreNamedField final : public HTemplateInstruction<3> {
   Handle<Map> transition_map() const {
     if (has_transition()) {
       return Handle<Map>::cast(
-          HConstant::cast(transition())->handle(Isolate::Current()));
+          HConstant::cast(transition())->handle(isolate()));
     } else {
       return Handle<Map>();
     }