Small cleanups in RegExp to avoid generating lots of code just because there is a try/catch in our …

sdk/lib/_internal/compiler/implementation/js_backend/backend.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/js_backend/backend.dart	(revision 19035)
+++ sdk/lib/_internal/compiler/implementation/js_backend/backend.dart	(working copy)
@@ -90,6 +90,7 @@
     HTypeList result = new HTypeList(node.inputs.length - 1);
     for (int i = 0; i < result.types.length; i++) {
       result.types[i] = node.inputs[i + 1].instructionType;
+      assert(!result.types[i].isConflicting());
     }
     return result;
   }
@@ -115,6 +116,7 @@
 
     for (int i = 0; i < result.types.length; i++) {
       result.types[i] = node.inputs[i + startInvokeIndex].instructionType;
+      assert(!result.types[i].isConflicting());
     }
     return result;
   }
@@ -276,6 +278,7 @@
                          Element field,
                          HType type) {
     assert(field.isField());
+    assert(!type.isConflicting());
     HType before = optimisticFieldType(field);
 
     HType oldType = typeMap[field];