Fix https://code.google.com/p/dart/issues/detail?id=15132, by not doing load elimination on typed a…

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 30337)
+++ sdk/lib/_internal/compiler/implementation/ssa/optimize.dart	(working copy)
@@ -1649,6 +1649,9 @@
 
   void visitIndexAssign(HIndexAssign instruction) {
     HInstruction receiver = instruction.receiver.nonCheck();
+    JavaScriptBackend backend = compiler.backend;
+    // Typed arrays may narrow incoming values.
+    if (backend.couldBeTypedArray(receiver.instructionType)) return;
     memorySet.registerKeyedValueUpdate(
         receiver, instruction.index, instruction.value);
   }