Remove uses of string + from API document generator.

lib/dartdoc/dartdoc.dart

Index: lib/dartdoc/dartdoc.dart
diff --git a/lib/dartdoc/dartdoc.dart b/lib/dartdoc/dartdoc.dart
index ea437d0dceaf4206b6adaa62f2d42625c805173f..36acef2f641c02d337656e71e70f11bbd49b5fc1 100644
--- a/lib/dartdoc/dartdoc.dart
+++ b/lib/dartdoc/dartdoc.dart
@@ -141,8 +141,8 @@ void main() {
     dartdoc.document(entrypoint);
   });
 
-  print('Documented ${dartdoc._totalLibraries} libraries, ' +
-      '${dartdoc._totalTypes} types, and ' +
+  print('Documented ${dartdoc._totalLibraries} libraries, '
+      '${dartdoc._totalTypes} types, and '
       '${dartdoc._totalMembers} members.');
 }
 
@@ -423,11 +423,11 @@ class Dartdoc {
     // Add data attributes describing what the page documents.
     var data = '';
     if (_currentLibrary != null) {
-      data += ' data-library="${md.escapeHtml(_currentLibrary.name)}"';
+      data = '$data data-library="${md.escapeHtml(_currentLibrary.name)}"';
     }
 
     if (_currentType != null) {
-      data += ' data-type="${md.escapeHtml(typeName(_currentType))}"';
+      data = '$data data-type="${md.escapeHtml(typeName(_currentType))}"';
     }
 
     write(
@@ -1096,7 +1096,7 @@ class Dartdoc {
 
     // TODO(rnystrom): Walks all the way up to root each time. Shouldn't do
     // this if the paths overlap.
-    return repeat('../', countOccurrences(_filePath, '/')) + fullPath;
+    return '${repeat('../', countOccurrences(_filePath, '/'))}$fullPath';
   }
 
   /** Gets whether or not the given URL is absolute or relative. */