[devtools] Support different encodings for Page.CaptureScreenshot.

ui/gfx/image/image_util_mac.mm

+// Copyright (c) 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/gfx/image/image_util.h"
+
+#import <Cocoa/Cocoa.h>
+
+#include "base/mac/scoped_nsobject.h"
+#include "ui/gfx/image/image.h"
+
+namespace gfx {
+
+bool JPEG1xEncodedDataFromImage(const Image& image,
+                                int quality,
+                                std::vector<unsigned char>* dst) {
+  if (!image.HasRepresentation(gfx::Image::kImageRepCocoa))
+    return JPEG1xEncodedDataFromSkiaRepresentation(image, quality, dst);
+
+  NSImage* nsImage = image.ToNSImage();
+
+  CGImageRef cgImage =
+      [nsImage CGImageForProposedRect:nil context:nil hints:nil];
+  base::scoped_nsobject<NSBitmapImageRep> rep(
+      [[NSBitmapImageRep alloc] initWithCGImage:cgImage]);
+
+  float compressionFactor = quality / 100.0;
+  NSDictionary* options = @{ NSImageCompressionFactor : @(compressionFactor)};
+  NSData* data =
+      [rep representationUsingType:NSJPEGFileType properties:options];
+
+  if ([data length] == 0)
+    return false;
+
+  dst->resize([data length]);
+  [data getBytes:&dst->at(0) length:[data length]];
+  return true;
+}
+
+}  // end namespace gfx