include benchmark.js in test suite (#1564)

- report file sizes and overall run time
- exit with non-zero code upon error

test/mocha/benchmark.js

@@ -0,0 +1,24 @@
+var assert = require("assert");
+var exec = require("child_process").exec;
+
+describe("test/benchmark.js", function() {
+    this.timeout(120000);
+    var command = '"' + process.argv[0] + '" test/benchmark.js ';
+    [
+        "-b",
+        "-b bracketize",
+        "-m",
+        "-mc passes=3",
+        "-mc passes=3,toplevel",
+        "-mc passes=3,unsafe",
+        "-mc keep_fargs=false,passes=3",
+        "-mc keep_fargs=false,passes=3,pure_getters,unsafe,unsafe_comps,unsafe_math,unsafe_proto",
+    ].forEach(function(args) {
+        it("Should pass with options " + args, function(done) {
+            exec(command + args, function(err) {
+                if (err) throw err;
+                done();
+            });
+        });
+    });
+});