Set ContentCache for created AnalysisContext(s) to control its view of the world.

pkg/analyzer/test/src/dart/analysis/driver_test.dart

 // Copyright (c) 2016, 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 analyzer.test.driver;
 
 import 'dart:async';
 import 'dart:convert';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 730 matching lines @@
     {
       AnalysisError error = result.errors[0];
       expect(error.offset, 13);
       expect(error.length, 2);
       expect(error.errorCode, HintCode.UNUSED_LOCAL_VARIABLE);
       expect(error.message, "The value of the local variable 'vv' isn't used.");
       expect(error.correction, "Try removing the variable, or using it.");
     }
   }
 
+  test_getResult_fileContentOverlay_throughAnalysisContext() async {
+    var a = _p('/test/bin/a.dart');
+    var b = _p('/test/bin/b.dart');
+
+    provider.newFile(a, 'import "b.dart";');
+    provider.newFile(b, 'var v = 1;');
+    contentOverlay[b] = 'var v = 2;';
+
+    var result = await driver.getResult(a);
+
+    // The content that was set into the overlay for "b" should be visible
+    // through the AnalysisContext that was used to analyze "a".
+    CompilationUnitElement unitA = result.unit.element;
+    Source sourceB = unitA.library.imports[0].importedLibrary.source;
+    expect(unitA.context.getContents(sourceB).data, 'var v = 2;');
+  }
+
   test_getResult_inferTypes_finalField() async {
     addTestFile(
         r'''
 class C {
   final f = 42;
 }
 ''',
         priority: true);
     await _waitForIdle();
 
@@ skipping 1016 matching lines @@
   String _p(String path) => provider.convertPath(path);
 
   Future<Null> _waitForIdle() async {
     await idleStatusMonitor.signal;
   }
 
   static String _md5(String content) {
     return hex.encode(md5.convert(UTF8.encode(content)).bytes);
   }
 }