Make String16 consturctors non-inline to save binary size (150kb)

test/js-perf-test/Inspector/runtime.js

+// Copyright 2017 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+(function() {
+  new BenchmarkSuite('Runtime.evaluate', [1000], [
+    new Benchmark('Runtime.evaluate', false, false, 0, EvaluateTest, Setup, TearDown),
+  ]);
+
+  function Setup() {
+    // Force lazy compilation of inspector related scripts.
+    SendMessage('Runtime.evaluate', {expression: ''});
+  }
+
+  function TearDown() {
+  }
+
+  function EvaluateTest() {
+    // This is meant to exercise the overhead of v8_inspector::String16
+    // constructors. https://crbug.com/738469
+    for (var i = 0; i < 10; ++i) {
+      SendMessage('Runtime.evaluate', {expression: '({})', returnByValue: true});
+    }
+  }
+})();