Refactor BackendHelpers to make 'find' methods private.

pkg/compiler/lib/src/js_backend/checked_mode_helpers.dart

Index: pkg/compiler/lib/src/js_backend/checked_mode_helpers.dart
diff --git a/pkg/compiler/lib/src/js_backend/checked_mode_helpers.dart b/pkg/compiler/lib/src/js_backend/checked_mode_helpers.dart
index 57487179f081d74d350f0662d6a136d2955eeebd..30c9fbdcd449842f32b427538a5766a9d83fccc3 100644
--- a/pkg/compiler/lib/src/js_backend/checked_mode_helpers.dart
+++ b/pkg/compiler/lib/src/js_backend/checked_mode_helpers.dart
@@ -21,7 +21,7 @@ class CheckedModeHelper {
   StaticUse getStaticUse(Compiler compiler) {
     JavaScriptBackend backend = compiler.backend;
     return new StaticUse.staticInvoke(
-        backend.helpers.findHelper(name), callStructure);
+        backend.helpers.jsHelperLibrary.find(name), callStructure);

[Siggi Cherem (dart-lang), 2017/01/03 17:05:37]

maybe add a TODO about fixing this one too?

It seems like you are trying to hide all the name manipulations inside backend
helpers, so eventually that would mean to change things a bit with how the
checkedModeHelpers are created? I'm guessing we would probably provide the
entity rather than the name, and move something like
`getCheckedModeHelperNameInternal` into the backend helpers?

[Johnni Winther, 2017/01/04 10:10:57]

Added a TODO. What we really need is to only create (and enqueue) this on need
instead of brute force. These should be created due to BackendFeatures.

   }
 
   CallStructure get callStructure => CallStructure.ONE_ARG;