Add access to FutureOr in TypeProviders (and add implementation in mock sdks)

pkg/analyzer/lib/src/generated/testing/test_type_provider.dart

Index: pkg/analyzer/lib/src/generated/testing/test_type_provider.dart
diff --git a/pkg/analyzer/lib/src/generated/testing/test_type_provider.dart b/pkg/analyzer/lib/src/generated/testing/test_type_provider.dart
index 953dcee3f328390123eddd88dc53f1f46688ebf7..c2a3a43320d9f52a655aac16f0629008fedcd108 100644
--- a/pkg/analyzer/lib/src/generated/testing/test_type_provider.dart
+++ b/pkg/analyzer/lib/src/generated/testing/test_type_provider.dart
@@ -64,6 +64,11 @@ class TestTypeProvider extends TypeProviderBase {
   InterfaceType _futureNullType;
 
   /**
+   * The type representing the built-in type 'FutureOr'
+   */
+  InterfaceType _futureOrType;
+
+  /**
    * The type representing the built-in type 'Future'
    */
   InterfaceType _futureType;
@@ -262,6 +267,26 @@ class TestTypeProvider extends TypeProviderBase {
   }
 
   @override
+  InterfaceType get futureOrType {
+    if (_futureOrType == null) {
+      Source asyncSource = _context.sourceFactory.forUri(DartSdk.DART_ASYNC);
+      _context.setContents(asyncSource, "");
+      CompilationUnitElementImpl asyncUnit =
+          new CompilationUnitElementImpl("async.dart");
+      LibraryElementImpl asyncLibrary = new LibraryElementImpl.forNode(
+          _context, AstTestFactory.libraryIdentifier2(["dart.async"]));
+      asyncLibrary.definingCompilationUnit = asyncUnit;
+      asyncUnit.librarySource = asyncUnit.source = asyncSource;
+
+      ClassElementImpl futureOr =
+          ElementFactory.classElement2("FutureOr", ["T"]);
+      _futureOrType = futureOr.type;
+      asyncUnit.types = <ClassElement>[futureOr];
+    }
+    return _futureOrType;
+  }
+
+  @override
   InterfaceType get futureType {
     if (_futureType == null) {
       Source asyncSource = _context.sourceFactory.forUri(DartSdk.DART_ASYNC);