Handle (missing) trailing slash in dartdoc

sdk/lib/_internal/dartdoc/lib/src/mirrors/dart2js_mirror.dart

Index: sdk/lib/_internal/dartdoc/lib/src/mirrors/dart2js_mirror.dart
diff --git a/sdk/lib/_internal/dartdoc/lib/src/mirrors/dart2js_mirror.dart b/sdk/lib/_internal/dartdoc/lib/src/mirrors/dart2js_mirror.dart
index a28bb7ff3aa628f1e8bd7147863e4c3e168f23f7..61e27b85dee175a3e12c682771e55648ae5f4997 100644
--- a/sdk/lib/_internal/dartdoc/lib/src/mirrors/dart2js_mirror.dart
+++ b/sdk/lib/_internal/dartdoc/lib/src/mirrors/dart2js_mirror.dart
@@ -339,10 +339,13 @@ class Dart2JsCompilation implements Compilation {
   Dart2JsCompilation(Path script, Path libraryRoot,
                      [Path packageRoot, List<String> opts = const <String>[]])
       : cwd = getCurrentDirectory(), sourceFiles = <String, SourceFile>{} {
-    var libraryUri = cwd.resolve(libraryRoot.toString());
+    // Ensure that the URI ends with a / an thus is interpreted as a directory.
+    var libraryUri = cwd.resolve(
+        libraryRoot.hasTrailingSeparator ? '$libraryRoot' : '$libraryRoot/');
     var packageUri;
     if (packageRoot != null) {
-      packageUri = cwd.resolve(packageRoot.toString());
+      packageUri = cwd.resolve(
+          libraryRoot.hasTrailingSeparator ? '$packageRoot' : '$packageRoot/');
     } else {
       packageUri = libraryUri;
     }
@@ -356,10 +359,13 @@ class Dart2JsCompilation implements Compilation {
   Dart2JsCompilation.library(List<Path> libraries, Path libraryRoot,
                      [Path packageRoot, List<String> opts = const <String>[]])
       : cwd = getCurrentDirectory(), sourceFiles = <String, SourceFile>{} {
-    var libraryUri = cwd.resolve(libraryRoot.toString());
+    // Ensure that the URI ends with a / an thus is interpreted as a directory.
+    var libraryUri = cwd.resolve(
+        libraryRoot.hasTrailingSeparator ? '$libraryRoot' : '$libraryRoot/');
     var packageUri;
     if (packageRoot != null) {
-      packageUri = cwd.resolve(packageRoot.toString());
+      packageUri = cwd.resolve(
+          libraryRoot.hasTrailingSeparator ? '$packageRoot' : '$packageRoot/');
     } else {
       packageUri = libraryUri;
     }