Fix bug where a parameter was mutated while it was still used.

lib/compiler/implementation/ssa/codegen.dart

Index: lib/compiler/implementation/ssa/codegen.dart
diff --git a/lib/compiler/implementation/ssa/codegen.dart b/lib/compiler/implementation/ssa/codegen.dart
index f91de80334263c91b8e09dd07330f177e3ae3da9..b19f4cf7663167981578256995a1ea18d38abe5b 100644
--- a/lib/compiler/implementation/ssa/codegen.dart
+++ b/lib/compiler/implementation/ssa/codegen.dart
@@ -172,12 +172,6 @@ class SsaCodeGenerator implements HVisitor {
     if (instruction is HPhi) {
       HPhi phi = instruction;
       Element element = phi.element;
-      if (element != null && element.kind == ElementKind.PARAMETER) {
-        name = parameterNames[element];
-        names[id] = name;
-        return name;
-      }
-
       String prefix;
       if (element !== null && !element.name.isEmpty()) {
         prefix = element.name.slowToString();