Support 'dart.library.X' env variables in the VM.

runtime/lib/bool.cc

Index: runtime/lib/bool.cc
diff --git a/runtime/lib/bool.cc b/runtime/lib/bool.cc
index b536ccfe2898ea8e60587505f2e62fbfc41a575d..dcb19525ef928edae4a9bcf2ad8d254629ecf889 100644
--- a/runtime/lib/bool.cc
+++ b/runtime/lib/bool.cc
@@ -21,7 +21,7 @@ DEFINE_NATIVE_ENTRY(Bool_fromEnvironment, 3) {
   GET_NATIVE_ARGUMENT(Bool, default_value, arguments->NativeArgAt(2));
   // Call the embedder to supply us with the environment.
   const String& env_value =
-      String::Handle(Api::CallEnvironmentCallback(thread, name));
+      String::Handle(Api::GetEnvironmentValue(thread, name));
   if (!env_value.IsNull()) {
     if (Symbols::True().Equals(env_value)) {
       return Bool::True().raw();