Simplify generated code for assert()

runtime/lib/errors_patch.dart

Index: runtime/lib/errors_patch.dart
diff --git a/runtime/lib/errors_patch.dart b/runtime/lib/errors_patch.dart
index 8c995a4d146537d169781e1a088bdb710545f0e2..faf342b66a1db9ba2e1dac802b1699d78182c846 100644
--- a/runtime/lib/errors_patch.dart
+++ b/runtime/lib/errors_patch.dart
@@ -26,9 +26,13 @@ class _AssertionError extends Error implements AssertionError {
   static _throwNew(int assertionStart, int assertionEnd)
       native "AssertionError_throwNew";
 
-  static _handleCondition(condition) {
-    if (condition is Function) return condition();
-    return condition;
+  static void _checkAssertion(condition, int start, int end) {
+    if (condition is Function) {
+      condition = condition();
+    }
+    if (!condition) {
+      _throwNew(start, end);
+    }
   }
 
   String toString() {