Avoid inserting new temporaries because of HTypeConversion nodes.

lib/compiler/implementation/ssa/codegen_helpers.dart

Index: lib/compiler/implementation/ssa/codegen_helpers.dart
===================================================================
--- lib/compiler/implementation/ssa/codegen_helpers.dart	(revision 7378)
+++ lib/compiler/implementation/ssa/codegen_helpers.dart	(working copy)
@@ -54,23 +54,13 @@
   // they would not be alive.
   void visitTypeGuard(HTypeGuard instruction) {}
 
-  // TODO(ngeoffray): This should not be needed. The codegen should
-  // cope better with this instruction.
-  void visitTypeConversion(HTypeConversion instruction) {}
+  void visitTypeConversion(HTypeConversion instruction) {
+    if (!instruction.checked) generateAtUseSite.add(instruction);
+    visitInstruction(instruction);
+  }
 
   void tryGenerateAtUseSite(HInstruction instruction) {
-    // A type guard should never be generate at use site, otherwise we
-    // cannot bailout.
-    if (instruction is HTypeGuard) return;
-
-    // A check should never be generate at use site, otherwise we
-    // cannot throw.
-    if (instruction is HCheck) return;
-
-    // TODO(ngeoffray): This should not be needed. The codegen should
-    // cope better with this instruction.
-    if (instruction is HTypeConversion) return;
-
+    if (instruction.isControlFlow()) return;
     generateAtUseSite.add(instruction);
   }