Add optional message to assert in Dart2js.

pkg/compiler/lib/src/ssa/builder.dart

Index: pkg/compiler/lib/src/ssa/builder.dart
diff --git a/pkg/compiler/lib/src/ssa/builder.dart b/pkg/compiler/lib/src/ssa/builder.dart
index 4a2f3e0de7ed64455e5387e51c9ff41b48e6a96d..9753787f7110b16d77dc54d53d526b9ebcd3a39d 100644
--- a/pkg/compiler/lib/src/ssa/builder.dart
+++ b/pkg/compiler/lib/src/ssa/builder.dart
@@ -2589,6 +2589,31 @@ class SsaBuilder extends ast.Visitor
     return pop();
   }
 
+  visitAssert(ast.Assert node) {
+    if (!compiler.enableUserAssertions) return;
+
+    void buildCondition() {
+      visit(node.condition);
+      var arguments = [pop()];
+      pushInvokeStatic(node, backend.assertConditionHelperMethod, arguments);
+    }
+    void fail() {
+      var arguments = new List();
+      if (node.message != null) {
+        visit(node.message);
+        arguments.add(pop());
+      } else {
+        arguments.add(graph.addConstantNull(compiler));
+      }
+      pushInvokeStatic(node, backend.assertThrowMethod, arguments);
+      pop();
+    }
+    handleIf(node,
+        visitCondition: buildCondition,
+        visitThen: () {},
+        visitElse: fail);
+  }
+
   visitBlock(ast.Block node) {
     assert(!isAborted());
     if (!isReachable) return;  // This can only happen when inlining.
@@ -5162,18 +5187,6 @@ class SsaBuilder extends ast.Visitor
     return false;
   }
 
-  @override
-  visitAssert(ast.Send node, ast.Node expression, _) {
-    if (!compiler.enableUserAssertions) {
-      stack.add(graph.addConstantNull(compiler));
-      return;
-    }
-    assert(invariant(node, node.arguments.tail.isEmpty,
-        message: "Invalid assertion: $node"));
-    generateStaticFunctionInvoke(
-        node, backend.assertMethod, CallStructure.ONE_ARG);
-  }
-
   visitStaticSend(ast.Send node) {
     internalError(node, "Unexpected visitStaticSend");
   }
@@ -8231,14 +8244,6 @@ class SsaBuilder extends ast.Visitor
   }
 
   @override
-  void errorInvalidAssert(
-      ast.Send node,
-      ast.NodeList arguments,
-      _) {
-    visitNode(node);
-  }
-
-  @override
   void errorUndefinedBinaryExpression(
       ast.Send node,
       ast.Node left,