[dart2dart] Make removal of asserts and forcing type strips go under

lib/compiler/implementation/dart_backend/backend.dart

Index: lib/compiler/implementation/dart_backend/backend.dart
diff --git a/lib/compiler/implementation/dart_backend/backend.dart b/lib/compiler/implementation/dart_backend/backend.dart
index a55e65211c3d229b18e58f8b0ace31d2af8da887..bef20f6d6e9b73d9d3cf9d2dc80c4c398b25418f 100644
--- a/lib/compiler/implementation/dart_backend/backend.dart
+++ b/lib/compiler/implementation/dart_backend/backend.dart
@@ -2,16 +2,15 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-const bool REMOVE_ASSERTS = false;
-
 class ElementAst {
   final Node ast;
   final TreeElements treeElements;
 
   ElementAst(this.ast, this.treeElements);
 
-  factory ElementAst.rewrite(compiler, ast, treeElements) {
-    final rewriter = new FunctionBodyRewriter(compiler, treeElements);
+  factory ElementAst.rewrite(compiler, ast, treeElements, stripAsserts) {
+    final rewriter =
+        new FunctionBodyRewriter(compiler, treeElements, stripAsserts);
     return new ElementAst(rewriter.visit(ast), rewriter.cloneTreeElements);
   }
 
@@ -63,8 +62,9 @@ class VariableListAst extends ElementAst {
 
 class FunctionBodyRewriter extends CloningVisitor {
   final Compiler compiler;
+  final bool stripAsserts;
 
-  FunctionBodyRewriter(this.compiler, originalTreeElements)
+  FunctionBodyRewriter(this.compiler, originalTreeElements, this.stripAsserts)
       : super(originalTreeElements);
 
   visitFunctionExpression(FunctionExpression node) {
@@ -74,7 +74,7 @@ class FunctionBodyRewriter extends CloningVisitor {
         Send send = statement.expression.asSend();
         if (send !== null) {
           Element element = originalTreeElements[send];
-          if (REMOVE_ASSERTS && element === compiler.assertMethod) {
+          if (stripAsserts && element === compiler.assertMethod) {
             return true;
           }
         }
@@ -114,7 +114,8 @@ class FunctionBodyRewriter extends CloningVisitor {
 
 class DartBackend extends Backend {
   final List<CompilerTask> tasks;
-  final bool forceCutDeclarationTypes;
+  final bool forceStripTypes;
+  final bool stripAsserts;
   // TODO(antonm): make available from command-line options.
   final bool outputAst = false;
 
@@ -187,8 +188,10 @@ class DartBackend extends Backend {
     return true;
   }
 
-  DartBackend(Compiler compiler, this.forceCutDeclarationTypes)
+  DartBackend(Compiler compiler, List<String> strips)
       : tasks = <CompilerTask>[],
+        forceStripTypes = strips.indexOf('types') != -1,
+        stripAsserts = strips.indexOf('asserts') != -1,
         super(compiler);
 
   void enqueueHelpers(Enqueuer world) {
@@ -306,8 +309,8 @@ class DartBackend extends Backend {
     resolvedElements.forEach((element, treeElements) {
       if (!shouldOutput(element)) return;
 
-      var elementAst =
-          new ElementAst.rewrite(compiler, parse(element), treeElements);
+      var elementAst = new ElementAst.rewrite(
+          compiler, parse(element), treeElements, stripAsserts);
       if (element.isField()) {
         final list = (element as VariableElement).variables;
         elementAst = elementAsts.putIfAbsent(
@@ -383,7 +386,7 @@ class DartBackend extends Backend {
     // Create renames.
     Map<Node, String> renames = new Map<Node, String>();
     Map<LibraryElement, String> imports = new Map<LibraryElement, String>();
-    bool shouldCutDeclarationTypes = forceCutDeclarationTypes
+    bool shouldCutDeclarationTypes = forceStripTypes
         || (compiler.enableMinification
             && isSafeToRemoveTypeDeclarations(classMembers));
     renamePlaceholders(