Move all flags to CompilerOptions (first step to stop passing the compiler to

pkg/compiler/lib/src/native/native.dart

Index: pkg/compiler/lib/src/native/native.dart
diff --git a/pkg/compiler/lib/src/native/native.dart b/pkg/compiler/lib/src/native/native.dart
index 4a1a641f6ee6e8668dc1c0189698ca936e5aac96..5a1af7cfe489e605c9e761428ef3b205038c827f 100644
--- a/pkg/compiler/lib/src/native/native.dart
+++ b/pkg/compiler/lib/src/native/native.dart
@@ -30,7 +30,7 @@ bool maybeEnableNative(Compiler compiler,
       || libraryName == 'dart:web_audio'
       || libraryName == 'dart:web_gl'
       || libraryName == 'dart:web_sql'
-      || compiler.allowNativeExtensions) {
+      || compiler.options.allowNativeExtensions) {
     return true;
   }
   return false;