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

pkg/analyzer_cli/lib/src/analyzer_impl.dart

 // Copyright (c) 2015, 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_cli.src.analyzer_impl;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:io';
 
@@ skipping 146 matching lines @@
     sources.clear();
     errorInfos.clear();
     Uri libraryUri = librarySource.uri;
     if (libraryUri.scheme == 'package' && libraryUri.pathSegments.length > 0) {
       _selfPackageName = libraryUri.pathSegments[0];
     }
   }
 
   Future<ErrorSeverity> _analyze(int printMode) async {
     // Don't try to analyze parts.
-    if (context.computeKindOf(librarySource) == SourceKind.PART) {
+    String path = librarySource.fullName;
+    SourceKind librarySourceKind = analysisDriver != null
+        ? await analysisDriver.getSourceKind(path)
+        : context.computeKindOf(librarySource);
+    if (librarySourceKind == SourceKind.PART) {
       stderr.writeln("Only libraries can be analyzed.");
-      stderr.writeln(
-          "${librarySource.fullName} is a part and can not be analyzed.");
+      stderr.writeln("${path} is a part and can not be analyzed.");
       return ErrorSeverity.ERROR;
     }
 
     LibraryElement libraryElement = await _resolveLibrary();
     prepareSources(libraryElement);
     await prepareErrors();
 
     // Print errors and performance numbers.
     if (printMode == 1) {
       _printErrors();
@@ skipping 198 matching lines @@
   }
 
   @override
   void logInformation(String message, [CaughtException exception]) {
     outSink.writeln(message);
     if (exception != null) {
       outSink.writeln(exception);
     }
   }
 }