Use declared variables to select the correct configuration for resolution

pkg/analyzer/lib/context/declared_variables.dart

Index: pkg/analyzer/lib/context/declared_variables.dart
diff --git a/pkg/analyzer/lib/context/declared_variables.dart b/pkg/analyzer/lib/context/declared_variables.dart
index 86d6234b436e586d238eb22cc2f0690a237dab8d..50c47ddca372dfdf2eb535cce628510abf76490a 100644
--- a/pkg/analyzer/lib/context/declared_variables.dart
+++ b/pkg/analyzer/lib/context/declared_variables.dart
@@ -35,6 +35,12 @@ class DeclaredVariables {
   }
 
   /**
+   * Return the raw string value of the variable with the given [name],
+   * or `null` of the variable is not defined.
+   */
+  String get(String name) => _declaredVariables[name];
+
+  /**
    * Return the value of the variable with the given [name] interpreted as a
    * 'boolean' value. If the variable is not defined (or [name] is `null`), a
    * DartObject representing "unknown" is returned. If the value cannot be