Implement AnalysisDriver.getSourceKind() and use it in analyzer-cli.

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 1099 matching lines @@
     Future<AnalysisResult> future2 = driver.getResult(testFile);
 
     // Both futures complete, with the same result.
     AnalysisResult result1 = await future1;
     AnalysisResult result2 = await future2;
     expect(result2, same(result1));
     expect(result1.path, testFile);
     expect(result1.unit, isNotNull);
   }
 
+  test_getSourceKind_library() async {
+    var path = _p('/test/lib/test.dart');
+    provider.newFile(path, 'class A {}');
+    expect(await driver.getSourceKind(path), SourceKind.LIBRARY);
+  }
+
+  test_getSourceKind_notDartFile() async {
+    var path = _p('/test/lib/test.txt');
+    provider.newFile(path, 'class A {}');
+    expect(await driver.getSourceKind(path), isNull);
+  }
+
+  test_getSourceKind_part() async {
+    var path = _p('/test/lib/test.dart');
+    provider.newFile(path, 'part of lib; class A {}');
+    expect(await driver.getSourceKind(path), SourceKind.PART);
+  }
+
   test_getTopLevelNameDeclarations() async {
     var a = _p('/test/lib/a.dart');
     var b = _p('/test/lib/b.dart');
     var c = _p('/test/lib/c.dart');
     var d = _p('/test/lib/d.dart');
 
     provider.newFile(a, 'class A {}');
     provider.newFile(b, 'export "a.dart", class B {}');
     provider.newFile(c, 'import "d.dart"; class C {}');
     provider.newFile(d, 'class D {}');
@@ skipping 847 matching lines @@
    * Return the [provider] specific path for the given Posix [path].
    */
   String _p(String path) => provider.convertPath(path);
 
   static String _md5(String content) {
     return hex.encode(md5.convert(UTF8.encode(content)).bytes);
   }
 }
 
 class _SourceMock extends TypedMock implements Source {}