Enable conditional directives by default.

pkg/compiler/lib/src/parser/parser.dart

Index: pkg/compiler/lib/src/parser/parser.dart
diff --git a/pkg/compiler/lib/src/parser/parser.dart b/pkg/compiler/lib/src/parser/parser.dart
index 41e756eaac013f4c43877485b54fc84cd77dc0bd..77236cc25f69b8b7c8e2ade096071a758fdfd107 100644
--- a/pkg/compiler/lib/src/parser/parser.dart
+++ b/pkg/compiler/lib/src/parser/parser.dart
@@ -183,11 +183,9 @@ class Parser {
   Token parseConditionalUris(Token token) {
     listener.beginConditionalUris(token);
     int count = 0;
-    if (parserOptions.enableConditionalDirectives) {
-      while (optional('if', token)) {
-        count++;
-        token = parseConditionalUri(token);
-      }
+    while (optional('if', token)) {
+      count++;
+      token = parseConditionalUri(token);
     }
     listener.endConditionalUris(count);
     return token;