Fix type of String.fromEnvironment() when the name is undefined.

pkg/analyzer/lib/src/generated/constant.dart

Index: pkg/analyzer/lib/src/generated/constant.dart
diff --git a/pkg/analyzer/lib/src/generated/constant.dart b/pkg/analyzer/lib/src/generated/constant.dart
index fa82b571354fa9a9dfddd115497662bb5c6f0982..b34a67854f6bd53e1ee2f71f7b6b3dda85981949 100644
--- a/pkg/analyzer/lib/src/generated/constant.dart
+++ b/pkg/analyzer/lib/src/generated/constant.dart
@@ -2425,7 +2425,8 @@ class DeclaredVariables {
   DartObject getString(TypeProvider typeProvider, String variableName) {
     String value = _declaredVariables[variableName];
     if (value == null) {
-      return new DartObjectImpl(typeProvider.intType, IntState.UNKNOWN_VALUE);
+      return new DartObjectImpl(typeProvider.stringType,
+          StringState.UNKNOWN_VALUE);
     }
     return new DartObjectImpl(typeProvider.stringType, new StringState(value));
   }