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

pkg/analyzer/lib/src/dart/analysis/driver.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.
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:typed_data';
 
 import 'package:analyzer/context/declared_variables.dart';
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 569 matching lines @@
     var completer = new Completer<AnalysisResult>();
     _requestedFiles
         .putIfAbsent(path, () => <Completer<AnalysisResult>>[])
         .add(completer);
     _statusSupport.transitionToAnalyzing();
     _scheduler._notify(this);
     return completer.future;
   }
 
   /**
+   * Return a [Future] that completes with the [SourceKind] for the Dart
+   * file with the given [path]. If the file is not a Dart file or cannot
+   * be analyzed, the [Future] completes with `null`.
+   *
+   * The [path] must be absolute and normalized.
+   */
+  Future<SourceKind> getSourceKind(String path) async {
+    if (AnalysisEngine.isDartFileName(path)) {
+      FileState file = _fsState.getFileForPath(path);
+      return file.isPart ? SourceKind.PART : SourceKind.LIBRARY;
+    }
+    return null;
+  }
+
+  /**
    * Return a [Future] that completes with top-level declarations with the
    * given [name] in all known libraries.
    */
   Future<List<TopLevelDeclarationInSource>> getTopLevelNameDeclarations(
       String name) {
     var task = new _TopLevelNameDeclarationsTask(this, name);
     _topLevelNameDeclarationsTasks.add(task);
     _statusSupport.transitionToAnalyzing();
     _scheduler._notify(this);
     return task.completer.future;
@@ skipping 1162 matching lines @@
           libraryDeclarations.add(new TopLevelDeclarationInSource(
               file.source, declaration, isExported));
         }
       }
     }
 
     // We're not done yet.
     return false;
   }
 }