Overhaul tree IR visitor and rename IR classes.

pkg/compiler/lib/src/js_backend/codegen/task.dart

Index: pkg/compiler/lib/src/js_backend/codegen/task.dart
diff --git a/pkg/compiler/lib/src/js_backend/codegen/task.dart b/pkg/compiler/lib/src/js_backend/codegen/task.dart
index d631f286655f710e1b4320367c062ff39a75fd0f..ac778d513b5a1a6bf8ddb50fc9a646c85d4c3a53 100644
--- a/pkg/compiler/lib/src/js_backend/codegen/task.dart
+++ b/pkg/compiler/lib/src/js_backend/codegen/task.dart
@@ -156,7 +156,7 @@ class CpsFunctionCompiler implements FunctionCompiler {
     }
   }
 
-  static bool checkCpsIntegrity(cps.ExecutableDefinition node) {
+  static bool checkCpsIntegrity(cps.RootNode node) {
     new CheckCpsIntegrity().check(node);
     return true; // So this can be used from assert().
   }
@@ -192,7 +192,7 @@ class CpsFunctionCompiler implements FunctionCompiler {
     return treeNode;
   }
 
-  static bool checkTreeIntegrity(tree_ir.ExecutableDefinition node) {
+  static bool checkTreeIntegrity(tree_ir.RootNode node) {
     new CheckTreeIntegrity().check(node);
     return true; // So this can be used from assert().
   }