Remove now unused --unparse-validation flag.

lib/compiler/implementation/compiler.dart

Index: lib/compiler/implementation/compiler.dart
diff --git a/lib/compiler/implementation/compiler.dart b/lib/compiler/implementation/compiler.dart
index 64295aaca7f88580fa37ff5805cdae173446f8f1..a7211b14496aaca2c53d1a931864838cf88addec 100644
--- a/lib/compiler/implementation/compiler.dart
+++ b/lib/compiler/implementation/compiler.dart
@@ -167,7 +167,6 @@ class Compiler implements DiagnosticListener {
             this.enableTypeAssertions = false,
             this.enableUserAssertions = false,
             bool emitJavascript = true,
-            validateUnparse = false,
             generateSourceMap = true])
       : libraries = new Map<String, LibraryElement>(),
         world = new World(),
@@ -185,7 +184,7 @@ class Compiler implements DiagnosticListener {
     typesTask = new ti.TypesTask(this);
     backend = emitJavascript ?
         new js_backend.JavaScriptBackend(this, generateSourceMap) :
-        new dart_backend.DartBackend(this, validateUnparse);
+        new dart_backend.DartBackend(this);
     enqueuer = new EnqueueTask(this);
     tasks = [scanner, dietParser, parser, resolver, closureToClassMapper,
              checker, typesTask, constantHandler, enqueuer];