Fix crash when using type parameters on custom elements

pkg/compiler/lib/src/ssa/locals_handler.dart

Index: pkg/compiler/lib/src/ssa/locals_handler.dart
diff --git a/pkg/compiler/lib/src/ssa/locals_handler.dart b/pkg/compiler/lib/src/ssa/locals_handler.dart
index 77fe43096593cfc86296c0983261e2dd8e7cfe1f..70d9522361a406ebf74ddf8c0071daae43bfce5d 100644
--- a/pkg/compiler/lib/src/ssa/locals_handler.dart
+++ b/pkg/compiler/lib/src/ssa/locals_handler.dart
@@ -276,6 +276,10 @@ class LocalsHandler {
           new HParameterValue(parameter, new TypeMask.exact(cls, closedWorld));
       builder.graph.explicitReceiverParameter = value;
       builder.graph.entry.addAtEntry(value);
+      if (builder.lastAddedParameter == null) {
+        // If this is the first parameter inserted, make sure it stays first.
+        builder.lastAddedParameter = value;
+      }
     }
   }