Change assert implementation to not depend on a top-level function called 'assert'.

lib/compiler/implementation/universe.dart

Index: lib/compiler/implementation/universe.dart
diff --git a/lib/compiler/implementation/universe.dart b/lib/compiler/implementation/universe.dart
index a03a61c7295d92f44e19ced9a4a85f67449360d7..a8e16e777c071336873cf11454f44a2edf1d9dea 100644
--- a/lib/compiler/implementation/universe.dart
+++ b/lib/compiler/implementation/universe.dart
@@ -165,6 +165,14 @@ class Selector implements Hashable {
   bool isUnaryOperator() => isOperator() && argumentCount == 0;
   bool isBinaryOperator() => isOperator() && argumentCount == 1;
 
+  /** Check whether this is a call to 'assert' with one positional parameter. */
+  bool isAssertSyntax() {
+    return (isCall() &&
+            name == const SourceString("assert") &&
+            argumentCount == 1 &&
+            namedArgumentCount == 0);
+  }
+
   int hashCode() => argumentCount + 1000 * namedArguments.length;
   int get namedArgumentCount => namedArguments.length;
   int get positionalArgumentCount => argumentCount - namedArgumentCount;
@@ -299,8 +307,9 @@ class Selector implements Hashable {
 
   bool operator ==(other) {
     if (other is !Selector) return false;
-    return receiverType === other.receiverType
-        && equalsUntyped(other);
+    Selector otherSelector = other;
+    return receiverType === otherSelector.receiverType
+        && equalsUntyped(otherSelector);
   }
 
   bool equalsUntyped(Selector other) {