Use the work element instead of the current element to satisfy unit tests.

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

Index: sdk/lib/_internal/compiler/implementation/ssa/optimize.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/ssa/optimize.dart	(revision 14732)
+++ sdk/lib/_internal/compiler/implementation/ssa/optimize.dart	(working copy)
@@ -39,7 +39,7 @@
           new SsaConstantFolder(constantSystem, backend, work, types),
           new SsaTypeConversionInserter(compiler),
           new SsaTypePropagator(compiler, types),
-          new SsaCheckInserter(backend, types, context.boundsChecked),
+          new SsaCheckInserter(backend, work, types, context.boundsChecked),
           new SsaConstantFolder(constantSystem, backend, work, types),
           new SsaRedundantPhiEliminator(),
           new SsaDeadPhiEliminator(),
@@ -81,7 +81,7 @@
           // Then run the [SsaCheckInserter] because the type propagator also
           // propagated types non-speculatively. For example, it might have
           // propagated the type array for a call to the List constructor.
-          new SsaCheckInserter(backend, types, context.boundsChecked)];
+          new SsaCheckInserter(backend, work, types, context.boundsChecked)];
       runPhases(graph, phases);
       return !work.guards.isEmpty;
     });
@@ -102,7 +102,7 @@
       // Also run the type propagator, to please the codegen in case
       // no other optimization is run.
       runPhases(graph, <OptimizationPhase>[
-          new SsaCheckInserter(backend, types, context.boundsChecked),
+          new SsaCheckInserter(backend, work, types, context.boundsChecked),
           new SsaTypePropagator(compiler, types)]);
     });
   }
@@ -651,17 +651,20 @@
   final HTypeMap types;
   final ConstantSystem constantSystem;
   final Set<HInstruction> boundsChecked;
+  final WorkItem work;
   final String name = "SsaCheckInserter";
   HGraph graph;
   Element lengthInterceptor;
   Selector lengthSelector;
 
-  SsaCheckInserter(JavaScriptBackend backend, this.types, this.boundsChecked)
+  SsaCheckInserter(JavaScriptBackend backend,
+                   this.work,
+                   this.types,
+                   this.boundsChecked)
       : constantSystem = backend.constantSystem {
     SourceString lengthString = const SourceString('length');
-    lengthSelector = new Selector.getter(
-        lengthString,
-        backend.compiler.currentElement.getLibrary());
+    lengthSelector =
+        new Selector.getter(lengthString, work.element.getLibrary());
     lengthInterceptor =
         backend.builder.interceptors.getStaticInterceptor(lengthSelector);
   }