Simplify the API for incremental_resolved_ast_generator.

pkg/front_end/lib/src/incremental_kernel_generator_impl.dart

 // Copyright (c) 2017, 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.
 
 import 'dart:async';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/standard_resolution_map.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/error/error.dart';
@@ skipping 75 matching lines @@
   }
 
   @override
   void invalidate(String path) => _resolvedAstGenerator.invalidate(path);
 
   @override
   void invalidateAll() => _resolvedAstGenerator.invalidateAll();
 }
 
 class _AnalysisContextProxy implements AnalysisContext {
-  final Map<Uri, ResolvedLibrary> _resolvedLibraries;
+  final Map<Uri, Map<Uri, CompilationUnit>> _resolvedLibraries;
 
   @override
   final _SourceFactoryProxy sourceFactory = new _SourceFactoryProxy();
 
   @override
   final AnalysisOptions analysisOptions;
 
   _AnalysisContextProxy(this._resolvedLibraries, this.analysisOptions);
 
   List<AnalysisError> computeErrors(Source source) {
     // TODO(paulberry): do we need to return errors sometimes?
     return [];
   }
 
   LibraryElement computeLibraryElement(Source source) {
     assert(_resolvedLibraries.containsKey(source.uri));
     return resolutionMap
         .elementDeclaredByCompilationUnit(
-            _resolvedLibraries[source.uri].definingCompilationUnit)
+            _resolvedLibraries[source.uri][source.uri])
         .library;
   }
 
   noSuchMethod(Invocation invocation) => unimplemented();
 
   CompilationUnit resolveCompilationUnit(
       Source unitSource, LibraryElement library) {
-    assert(_resolvedLibraries.containsKey(library.source.uri));
-    var resolvedLibrary = _resolvedLibraries[library.source.uri];
-    if (unitSource == library.source) {
-      return resolvedLibrary.definingCompilationUnit;
-    } else {
-      assert(resolvedLibrary.partUnits.containsKey(unitSource.uri));
-      return resolvedLibrary.partUnits[unitSource.uri];
-    }
+    var unit = _resolvedLibraries[library.source.uri][unitSource.uri];
+    assert(unit != null);
+    return unit;
   }
 }
 
 class _AnalysisOptionsProxy implements AnalysisOptions {
   final bool strongMode;
 
   _AnalysisOptionsProxy(this.strongMode);
 
   noSuchMethod(Invocation invocation) => unimplemented();
 }
 
 class _SourceFactoryProxy implements SourceFactory {
   Source forUri2(Uri absoluteUri) => new _SourceProxy(absoluteUri);
 
   noSuchMethod(Invocation invocation) => unimplemented();
 }
 
 class _SourceProxy extends BasicSource {
   _SourceProxy(Uri uri) : super(uri);
 
   noSuchMethod(Invocation invocation) => unimplemented();
 }