Use failedAt in more places

pkg/compiler/lib/src/apiimpl.dart

Index: pkg/compiler/lib/src/apiimpl.dart
diff --git a/pkg/compiler/lib/src/apiimpl.dart b/pkg/compiler/lib/src/apiimpl.dart
index 490bccc9444ec6fd73443841400031fc6758b815..ec504bb556f0102c6811351aa14d26c6fca0c3aa 100644
--- a/pkg/compiler/lib/src/apiimpl.dart
+++ b/pkg/compiler/lib/src/apiimpl.dart
@@ -377,9 +377,8 @@ class _Environment implements Environment {
   _Environment(this.definitions);
 
   String valueOf(String name) {
-    assert(invariant(
-        NO_LOCATION_SPANNABLE, compiler.resolvedUriTranslator != null,
-        message: "setupSdk() has not been run"));
+    assert(compiler.resolvedUriTranslator != null,
+        failedAt(NO_LOCATION_SPANNABLE, "setupSdk() has not been run"));
 
     var result = definitions[name];
     if (result != null || definitions.containsKey(name)) return result;