dart2js implementation of StringBuffer.writeAll that optimizes better

runtime/lib/string_buffer_patch.dart

Index: runtime/lib/string_buffer_patch.dart
diff --git a/runtime/lib/string_buffer_patch.dart b/runtime/lib/string_buffer_patch.dart
index a952f8aa730484d3baa7c641ca882e7e660cccc8..6991ead060e0225bb5734b9166d7683c6f3d5f65 100644
--- a/runtime/lib/string_buffer_patch.dart
+++ b/runtime/lib/string_buffer_patch.dart
@@ -91,6 +91,27 @@ patch class StringBuffer {
     }
   }
 
+  /* patch */ void writeAll(Iterable objects, [String separator = ""]) {
+    Iterator iterator = objects.iterator;
+    if (!iterator.moveNext()) return;
+    if (separator.isEmpty) {
+      do {
+        write(iterator.current);
+      } while (iterator.moveNext());
+    } else {
+      write(iterator.current);
+      while (iterator.moveNext()) {
+        write(separator);
+        write(iterator.current);
+      }
+    }
+  }
+
+  /* patch */ void writeln([Object obj = ""]) {
+    write(obj);
+    write("\n");
+  }
+
   /** Makes the buffer empty. */
   /* patch */ void clear() {
     _parts = null;