- Refactor the way X.fromEnvironment is implemented.

runtime/lib/bool.cc

Index: runtime/lib/bool.cc
===================================================================
--- runtime/lib/bool.cc	(revision 39888)
+++ runtime/lib/bool.cc	(working copy)
@@ -21,25 +21,15 @@
   GET_NON_NULL_NATIVE_ARGUMENT(String, name, arguments->NativeArgAt(1));
   GET_NATIVE_ARGUMENT(Bool, default_value, arguments->NativeArgAt(2));
   // Call the embedder to supply us with the environment.
-  Api::Scope api_scope(isolate);
-  Dart_EnvironmentCallback callback = isolate->environment_callback();
-  if (callback != NULL) {
-    Dart_Handle result = callback(Api::NewHandle(isolate, name.raw()));
-    if (Dart_IsString(result)) {
-      const char *chars;
-      Dart_StringToCString(result, &chars);
-      if (strcmp("true", chars) == 0) return Bool::True().raw();
-      if (strcmp("false", chars) == 0) return Bool::False().raw();
-    } else if (Dart_IsError(result)) {
-      const Object& error =
-          Object::Handle(isolate, Api::UnwrapHandle(result));
-      Exceptions::ThrowArgumentError(
-          String::Handle(
-              String::New(Error::Cast(error).ToErrorCString())));
-    } else if (!Dart_IsNull(result)) {
-      Exceptions::ThrowArgumentError(
-          String::Handle(String::New("Illegal environment value")));
+  const String& env_value =
+      String::Handle(Api::CallEnvironmentCallback(isolate, name));
+  if (!env_value.IsNull()) {
+    if (Symbols::True().Equals(env_value)) {
+      return Bool::True().raw();
     }
+    if (Symbols::False().Equals(env_value)) {
+      return Bool::False().raw();
+    }
   }
   return default_value.raw();
 }