Stop resolving all of js_helper unconditionally.

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

Index: sdk/lib/_internal/compiler/implementation/compiler.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/compiler.dart	(revision 18614)
+++ sdk/lib/_internal/compiler/implementation/compiler.dart	(working copy)
@@ -126,8 +126,24 @@
     return new ItemCompilationContext();
   }
 
-  SourceString getCheckedModeHelper(DartType type) => null;
+  // The following methods are hooks for the backend to register its
+  // helper methods.

[ahe, 2013/02/18 12:38:04]

Categories like this doesn't work, what happens if a method is added after them?

I would prefer if you could add real documentation comments to each of the
methods.

For example:

/// Called during resolution (and SSA graph building?) to record that [cls] was
instantiated from [element].
void registerInstantiatedClass(Element user, ClassElement cls, Enqueuer world)
{}

   void registerInstantiatedClass(ClassElement cls, Enqueuer enqueuer) {}
+  void registerStringInterpolation() {}

[ahe, 2013/02/18 12:38:04]

I think all of the following methods should take the element which add the
dependency. This will help us shortly when we start looking at dynamic
recompilation.

+  void registerCatchStatement() {}
+  void registerThrow() {}
+  void registerLazyField() {}
+  void registerTypeLiteral() {}
+  void registerStackTraceInCatch() {}
+  void registerIsCheck(DartType type, Enqueuer enqueuer) {}
+  void registerAsCheck(DartType type) {}
+  void registerThrowNoSuchMethod() {}
+  void registerThrowRuntimeError() {}
+  void registerAbstractClassInstantiation() {}
+  void registerFallThroughError() {}
+  void registerSuperNoSuchMethod() {}
+  void registerConstantMap() {}
+  void registerRuntimeType() {}
 }
 
 /**