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() {
+    SendMessage('Debugger.enable');

[kozy, 2017/07/06 21:18:32]

You don't need to enable Debugger to run Runtime.evaluate.

[agrieve, 2017/07/07 18:34:49]

Done.

+  }
+
+  function TearDown() {
+    SendMessage('Debugger.disable');
+  }
+
+  function EvaluateTest() {
+    for (var i = 0; i < 10; ++i) {
+      let result = SendMessage('Runtime.evaluate', {expression: '"foo"'});

[kozy, 2017/07/06 21:18:32]

I was experimenting with callgrind and tried to maximize time which we spend in
String16 cstor and in maximum got 5% time, I hope it will give us at least 10%
in string16 cstors in benchmark (since 5% it's for all code including shell
startup and everything else) and will make it useful:

SendMessage('Runtime.evaluate', {expression: '({})', returnByValue: true});

You actually don't need to check result of this method since we only measure
performance here.

[agrieve, 2017/07/07 18:34:49]

Done.

+      if (result.result.result.value != 'foo') {
+        throw new Error('eval response was: ' + JSON.stringify(result.result));
+      }
+    }
+  }
+})();