Handle (missing) trailing slash in dartdoc

sdk/lib/_internal/compiler/implementation/apiimpl.dart

 // Copyright (c) 2012, 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 leg_apiimpl;
 
 import 'dart:uri';
 
 import '../compiler.dart' as api;
 import 'dart2jslib.dart' as leg;
@@ skipping 16 matching lines @@
       : this.options = options,
         super(
             tracer: new ssa.HTracer(),
             enableTypeAssertions: hasOption(options, '--enable-checked-mode'),
             enableUserAssertions: hasOption(options, '--enable-checked-mode'),
             enableMinification: hasOption(options, '--minify'),
             emitJavaScript: !hasOption(options, '--output-type=dart'),
             disallowUnsafeEval: hasOption(options, '--disallow-unsafe-eval'),
             strips: getStrips(options),
             enableConcreteTypeInference:
-              hasOption(options, '--enable-concrete-type-inference'));
+              hasOption(options, '--enable-concrete-type-inference')) {
+    if (!libraryRoot.path.endsWith("/")) {
+      throw new ArgumentError("libraryRoot must end with a /");
+    }
+    if (packageRoot != null && !packageRoot.path.endsWith("/")) {
+      throw new ArgumentError("packageRoot must end with a /");
+    }
+  }
 
   static List<String> getStrips(List<String> options) {
     for (String option in options) {
       if (option.startsWith('--force-strip=')) {
         return option.substring('--force-strip='.length).split(',');
       }
     }
     return [];
   }
 
@@ skipping 113 matching lines @@
       handler(translateUri(span.uri, null), span.begin, span.end,
               message, kind);
     }
   }
 
   bool get isMockCompilation {
     return mockableLibraryUsed
       && (options.indexOf('--allow-mock-compilation') != -1);
   }
 }