Refactor the way we emit no such method handlers so it's easier to optimize it later.

lib/compiler/implementation/namer.dart

Index: lib/compiler/implementation/namer.dart
diff --git a/lib/compiler/implementation/namer.dart b/lib/compiler/implementation/namer.dart
index 526a9d1952f059dfbb36ee1a83d070ea2846f44c..0560a0aac2316d8affbd4907402658416758e40e 100644
--- a/lib/compiler/implementation/namer.dart
+++ b/lib/compiler/implementation/namer.dart
@@ -20,11 +20,13 @@ class Namer {
 
   Map<Element, String> globals;
   Map<String, int> usedGlobals;
+  Map<String, Set<LibraryElement>> usedPrivateNames;
   Map<String, LibraryElement> shortPrivateNameOwners;
 
   Namer(this.compiler)
       : globals = new Map<Element, String>(),
         usedGlobals = new Map<String, int>(),
+        usedPrivateNames = new Map<String, Set<LibraryElement>>(),
         shortPrivateNameOwners = new Map<String, LibraryElement>();
 
   final String CURRENT_ISOLATE = @'$';
@@ -78,6 +80,13 @@ class Namer {
     if (name.isPrivate()) {
       String nameString = name.slowToString();
 
+      // TODO(kasperl): This is a bit of a hacky way of keeping track
+      // of the libraries that use a particular private name.
+      Set<LibraryElement> usedBy =
+          usedPrivateNames.putIfAbsent(nameString, () =>
+                                       new Set<LibraryElement>());
+      usedBy.add(lib);
+
       // The first library asking for a short private name wins.
       LibraryElement owner =
           shortPrivateNameOwners.putIfAbsent(nameString, () => lib);