Remove unnecessary casts and general code clean-up

pkg/analyzer/lib/src/context/cache.dart

Index: pkg/analyzer/lib/src/context/cache.dart
diff --git a/pkg/analyzer/lib/src/context/cache.dart b/pkg/analyzer/lib/src/context/cache.dart
index 8be0a41b658a3b034501ba2ec492024fec44c3a4..f539e2ed193549209e3d6ba4f9421ec6678dc7c6 100644
--- a/pkg/analyzer/lib/src/context/cache.dart
+++ b/pkg/analyzer/lib/src/context/cache.dart
@@ -315,9 +315,7 @@ class CacheEntry {
       new HashMap<ResultDescriptor, ResultData>();
 
   CacheEntry(this.target) {
-    if (target is ElementImpl) {
-      (target as ElementImpl).setModifier(Modifier.CACHE_KEY, true);
-    }
+    _markAsCacheKey(target);
   }
 
   /**
@@ -632,6 +630,15 @@ class CacheEntry {
   }
 
   /**
+   * If the given `target` is an element, mark it as being a cache key.
+   */
+  void _markAsCacheKey(AnalysisTarget target) {
+    if (target is ElementImpl) {
+      target.setModifier(Modifier.CACHE_KEY, true);
+    }
+  }
+
+  /**
    * Set the [dependedOn] on which this result depends.
    */
   void _setDependedOnResults(ResultData thisData, TargetedResult thisResult,