Fix fromEnvironment when called from isolates.

runtime/lib/integers.cc

Index: runtime/lib/integers.cc
diff --git a/runtime/lib/integers.cc b/runtime/lib/integers.cc
index 4e64ea5ae04a625956daee125dd9f2c7cf296d94..07943aa8b0d71017581e4086da0f7b3167f620dd 100644
--- a/runtime/lib/integers.cc
+++ b/runtime/lib/integers.cc
@@ -239,6 +239,7 @@ DEFINE_NATIVE_ENTRY(Integer_fromEnvironment, 3) {
   GET_NON_NULL_NATIVE_ARGUMENT(String, name, arguments->NativeArgAt(1));
   GET_NATIVE_ARGUMENT(Integer, default_value, arguments->NativeArgAt(2));
   // Call the embedder to supply us with the environment.
+  Dart_EnterScope();
   Dart_EnvironmentCallback callback = isolate->environment_callback();
   if (callback != NULL) {
     Dart_Handle response = callback(Api::NewHandle(isolate, name.raw()));
@@ -261,6 +262,7 @@ DEFINE_NATIVE_ENTRY(Integer_fromEnvironment, 3) {
           String::Handle(String::New("Illegal environment value")));
     }
   }
+  Dart_ExitScope();
   return default_value.raw();
 }