Enable building headless_shell in MAC. This is an initial implementation with a hidden window, rath…

headless/lib/browser/headless_browser_impl_mac.mm

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "headless/lib/browser/headless_browser_impl.h"
+
+#include "content/public/browser/web_contents.h"
+#include "ui/base/cocoa/base_view.h"
+
+namespace headless {
+
+void HeadlessBrowserImpl::PlatformInitialize() {}
+
+void HeadlessBrowserImpl::PlatformCreateWindow() {}
+
+void HeadlessBrowserImpl::PlatformInitializeWebContents(
+    const gfx::Size& initial_size,
+    content::WebContents* web_contents) {
+  NSView* web_view = web_contents->GetNativeView();
+  [web_view setAutoresizingMask:(NSViewWidthSizable | NSViewHeightSizable)];
+
+  NSRect frame = NSMakeRect(0, 0, initial_size.width(), initial_size.height());
+  [web_view setFrame:frame];
+  return;
+}
+
+}  // namespace headless