Remove many explicit references to AnalysisContextImpl and enable testing of the new task model

pkg/analyzer/test/generated/incremental_resolver_test.dart

 // Copyright (c) 2014, 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.
 
 library engine.incremental_resolver_test;
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/error.dart';
@@ skipping 2453 matching lines @@
   }
 }
 
 @reflectiveTest
 class IncrementalResolverTest extends ResolverTestCase {
   Source source;
   String code;
   LibraryElement library;
   CompilationUnit unit;
 
+  @override
+  void reset() {
+    analysisContext2 = AnalysisContextFactory.oldContextWithCore();
+  }
+
+  @override
+  void resetWithOptions(AnalysisOptions options) {
+    analysisContext2 =
+        AnalysisContextFactory.oldContextWithCoreAndOptions(options);
+  }
+
   void setUp() {
     super.setUp();
     test_resolveApiChanges = true;
     log.logger = log.NULL_LOGGER;
   }
 
   void test_classMemberAccessor_body() {
     _resolveUnit(r'''
 class A {
   int get test {
@@ skipping 311 matching lines @@
     // update tokens
     {
       int delta = edit.replacement.length - edit.length;
       _shiftTokens(unit.beginToken, offset, delta);
     }
     // do incremental resolution
     int updateOffset = edit.offset;
     int updateEndOld = updateOffset + edit.length;
     int updateOldNew = updateOffset + edit.replacement.length;
     IncrementalResolver resolver = new IncrementalResolver(
-        analysisContext2.getReadableSourceEntryOrNull(source), null, null,
-        unit.element, updateOffset, updateEndOld, updateOldNew);
+        (analysisContext2 as AnalysisContextImpl)
+            .getReadableSourceEntryOrNull(source), null, null, unit.element,
+        updateOffset, updateEndOld, updateOldNew);
     bool success = resolver.resolve(newNode);
     expect(success, isTrue);
     List<AnalysisError> newErrors = analysisContext.computeErrors(source);
     // resolve "newCode" from scratch
     CompilationUnit fullNewUnit;
     {
       source = addSource(newCode);
       _runTasks();
       LibraryElement library = resolve(source);
       fullNewUnit = resolveCompilationUnit(source, library);
@@ skipping 1327 matching lines @@
     return ResolutionContextBuilder.contextFor(node, listener).scope;
   }
 }
 
 class _Edit {
   final int offset;
   final int length;
   final String replacement;
   _Edit(this.offset, this.length, this.replacement);
 }