Add support for tasks to determine whether they are appropriate for a given target

pkg/analyzer/test/src/task/model_test.dart

Index: pkg/analyzer/test/src/task/model_test.dart
diff --git a/pkg/analyzer/test/src/task/model_test.dart b/pkg/analyzer/test/src/task/model_test.dart
index 4db1ee2fef5aed8c5e2f5a10f770d5b042325522..0ea406e752d8047f5ba26738b9b2a9c83e39b90d 100644
--- a/pkg/analyzer/test/src/task/model_test.dart
+++ b/pkg/analyzer/test/src/task/model_test.dart
@@ -103,7 +103,7 @@ class SimpleResultCachingPolicyTest extends EngineTestCase {
 
 @reflectiveTest
 class TaskDescriptorImplTest extends EngineTestCase {
-  test_create() {
+  test_create_noOptionalArgs() {
     String name = 'name';
     BuildTask buildTask = (context, target) {};
     CreateTaskInputs createTaskInputs = (target) {};
@@ -114,12 +114,30 @@ class TaskDescriptorImplTest extends EngineTestCase {
     expect(descriptor.name, name);
     expect(descriptor.buildTask, equals(buildTask));
     expect(descriptor.createTaskInputs, equals(createTaskInputs));
+    expect(descriptor.isAppropriateFor(null), isTrue);
+    expect(descriptor.results, results);
+  }
+
+  test_create_withIsAppropriateFor() {
+    String name = 'name';
+    BuildTask buildTask = (context, target) {};
+    CreateTaskInputs createTaskInputs = (target) {};
+    List<ResultDescriptor> results = <ResultDescriptor>[];
+    IsAppropriateFor isAppropriateFor = (target) => false;
+    TaskDescriptorImpl descriptor = new TaskDescriptorImpl(
+        name, buildTask, createTaskInputs, results,
+        isAppropriateFor: isAppropriateFor);
+    expect(descriptor, isNotNull);
+    expect(descriptor.name, name);
+    expect(descriptor.buildTask, equals(buildTask));
+    expect(descriptor.createTaskInputs, equals(createTaskInputs));
+    expect(descriptor.isAppropriateFor(null), isFalse);
     expect(descriptor.results, results);
   }
 
   test_createTask() {
-    BuildTask buildTask = (context, target) =>
-        new TestAnalysisTask(context, target);
+    BuildTask buildTask =
+        (context, target) => new TestAnalysisTask(context, target);
     CreateTaskInputs createTaskInputs = (target) {};
     List<ResultDescriptor> results = <ResultDescriptor>[];
     TaskDescriptorImpl descriptor =