Change assert implementation to not depend on a top-level function called 'assert'.

lib/compiler/implementation/compiler.dart

Index: lib/compiler/implementation/compiler.dart
diff --git a/lib/compiler/implementation/compiler.dart b/lib/compiler/implementation/compiler.dart
index b1a49dfa368cd2e931138d46a86f2184a39f5c20..d7add0eae62f67d94f3374915f5041c9e0e25eaf 100644
--- a/lib/compiler/implementation/compiler.dart
+++ b/lib/compiler/implementation/compiler.dart
@@ -203,6 +203,10 @@ class Compiler implements DiagnosticListener {
     tasks.addAll(backend.tasks);
   }
 
+  // TODO(floitsch): remove once the compile-time constant handler doesn't
+  // depend on it anymore.
+  js_backend.Namer get namer => (backend as js_backend.JavaScriptBackend).namer;
+
   Universe get resolverWorld => enqueuer.resolution.universe;
   Universe get codegenWorld => enqueuer.codegen.universe;
 
@@ -359,7 +363,7 @@ class Compiler implements DiagnosticListener {
     libraries['dart:core'] = coreLibrary;
     libraries['dart:coreimpl'] = coreImplLibrary;
 
-    assertMethod = coreLibrary.find(const SourceString('assert'));
+    assertMethod = jsHelperLibrary.find(const SourceString('assert'));
 
     initializeSpecialClasses();
   }