Fix dart analyzer warnings.

tools/dom/src/html_native_DOMImplementation.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of html;
 
 class _Property {
   _Property(this.name) :
       _hasValue = false,
       writable = false,
@@ skipping 504 matching lines @@
     return (methodMirror.isGetter || methodMirror.isSetter) &&
           (methodMirror.isSynthetic ||
               _isSideEffectFreeGetter(methodMirror,libraryMirror));
   }
 
   // TODO(jacobr): generate more concise function descriptions instead of
   // dumping the entire function source.
   static String describeFunction(function) {
     if (function is _Trampoline) return function._methodMirror.source;
     try {
-      return reflect(function).function.source;
+      var mirror = reflect(function);
+      return mirror.function.source;
     } catch (e) {
       return function.toString();
     }
   }
 
   static List getInvocationTrampolineDetails(_Trampoline method) {
     var loc = method._methodMirror.location;
     return [loc.line, loc.column, loc.sourceUri.toString(),
         MirrorSystem.getName(method._selector)];
   }
@@ skipping 84 matching lines @@
           return;
         }
         var property = properties.putIfAbsent(name, () => new _Property(name));
         _fillMethodMirrorProperty(libraryMirror, classMirror, methodMirror,
             symbol, accessorPropertiesOnly, property);
       }
     });
   }
 
   static void _fillMethodMirrorProperty(LibraryMirror libraryMirror,
-        Mirror methodOwner, MethodMirror methodMirror, Symbol symbol,
+        methodOwner, MethodMirror methodMirror, Symbol symbol,
         bool accessorPropertiesOnly, _Property property) {
     if (methodMirror.isRegularMethod) {
       property
           ..value = new _MethodTrampoline(methodOwner, methodMirror, symbol)
           ..isMethod = true;
     } else if (methodMirror.isGetter) {
       if (treatPropertyAsField(methodMirror, libraryMirror)) {
         try {
           property.value = methodOwner.getField(symbol).reflectee;
         } catch (e) {
@@ skipping 25 matching lines @@
    * shown or hidden. [ownProperties] is not currently used but is part of the
    * Blink devtools API for enumerating properties.
    */
   static void _addInstanceMirrors(
       ObjectMirror objectMirror,
       LibraryMirror libraryMirror,
       Map<Symbol, Mirror> declarations,
       bool ownProperties, bool accessorPropertiesOnly,
       bool hideFields, bool hideMethods,
       Map<String, _Property> properties) {
-    declarations.forEach((Symbol symbol, Mirror declaration) {
+    declarations.forEach((symbol, declaration) {
       if (declaration is TypedefMirror || declaration is ClassMirror) return;
       var name = _getShortSymbolName(symbol, declaration);
       if (name.isEmpty) return;
       bool isField = declaration is VariableMirror ||
           (declaration is MethodMirror &&
               treatPropertyAsField(declaration, libraryMirror));
       if ((isField && hideFields) || (hideMethods && !isField)) return;
       if (accessorPropertiesOnly) {
         if (declaration is VariableMirror || declaration.isRegularMethod ||
             isField) {
@@ skipping 293 matching lines @@
   _scheduleImmediateHelper._schedule(callback);
 };
 
 get _pureIsolateScheduleImmediateClosure => ((void callback()) =>
   throw new UnimplementedError("scheduleMicrotask in background isolates "
                                "are not supported in the browser"));
 
 void _initializeCustomElement(Element e) {
   _Utils.initializeCustomElement(e);
 }