[devtools] Support different encodings for Page.CaptureScreenshot.

ui/snapshot/snapshot.cc

+// 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 "ui/snapshot/snapshot.h"
+
+#include "base/bind.h"
+#include "base/callback.h"
+#include "base/task_runner_util.h"
+#include "ui/gfx/image/image.h"
+
+namespace ui {
+
+namespace {
+
+scoped_refptr<base::RefCountedMemory> EncodeImage(const gfx::Image& image) {
+  return image.As1xPNGBytes();
+}
+
+void EncodeImageAndSchedulePNGCallback(
+    scoped_refptr<base::TaskRunner> background_task_runner,
+    const GrabWindowSnapshotAsyncPNGCallback& callback,
+    const gfx::Image& image) {
+  base::PostTaskAndReplyWithResult(background_task_runner.get(), FROM_HERE,
+                                   base::Bind(EncodeImage, image), callback);
+}
+
+}  // namespace
+
+void GrabWindowSnapshotAsyncPNG(
+    gfx::NativeWindow window,
+    const gfx::Rect& source_rect,
+    scoped_refptr<base::TaskRunner> background_task_runner,
+    const GrabWindowSnapshotAsyncPNGCallback& callback) {
+  GrabWindowSnapshotAsync(
+      window, source_rect,
+      base::Bind(EncodeImageAndSchedulePNGCallback,
+                 std::move(background_task_runner), callback));
+}
+
+}  // namespace ui