Add optional writeAll separator argument.

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

Index: sdk/lib/_internal/compiler/implementation/code_buffer.dart
diff --git a/sdk/lib/_internal/compiler/implementation/code_buffer.dart b/sdk/lib/_internal/compiler/implementation/code_buffer.dart
index 69fab9ae5ffd0a5d63ad071257cefff44c553857..4c0a1fe18c0efddc2b4039cd84a54190af215804 100644
--- a/sdk/lib/_internal/compiler/implementation/code_buffer.dart
+++ b/sdk/lib/_internal/compiler/implementation/code_buffer.dart
@@ -37,9 +37,19 @@ class CodeBuffer implements StringBuffer {
     return this;
   }
 
-  CodeBuffer writeAll(Iterable<Object> objects) {
-    for (var object in objects) {
-      write(object);
+  CodeBuffer writeAll(Iterable<Object> objects, [String separator = ""]) {
+    Iterator iterator = objects.iterator;
+    if (!iterator.moveNext()) return this;
+    if (separator == "") {
+      do {
+        write(iterator.current);
+      } while (iterator.moveNext());
+    } else {
+      buffer.write(iterator.current);
+      while (iterator.moveNext()) {
+        write(separator);
+        write(iterator.current);
+      }
     }
     return this;
   }