Support the DPR header for client hints.

Source/core/fetch/ImageResource.cpp

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller (mueller@kde.org)
     Copyright (C) 2002 Waldo Bastian (bastian@kde.org)
     Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
     Copyright (C) 2004, 2005, 2006, 2007 Apple Inc. All rights reserved.
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
     version 2 of the License, or (at your option) any later version.
 
     This library is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     Library General Public License for more details.
 
     You should have received a copy of the GNU Library General Public License
     along with this library; see the file COPYING.LIB.  If not, write to
     the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
     Boston, MA 02110-1301, USA.
 */
 
 #include "config.h"
 #include "core/fetch/ImageResource.h"
 
+#include "RuntimeEnabledFeatures.h"
 #include "core/fetch/ImageResourceClient.h"
 #include "core/fetch/MemoryCache.h"
 #include "core/fetch/ResourceClient.h"
 #include "core/fetch/ResourceClientWalker.h"
 #include "core/fetch/ResourceFetcher.h"
 #include "core/frame/FrameView.h"
 #include "core/platform/graphics/BitmapImage.h"
 #include "core/rendering/RenderObject.h"
 #include "core/svg/graphics/SVGImage.h"
 #include "platform/SharedBuffer.h"
 #include "wtf/CurrentTime.h"
 #include "wtf/StdLibExtras.h"
 #include "wtf/Vector.h"
 
 using namespace std;
 
 namespace WebCore {
 
 ImageResource::ImageResource(const ResourceRequest& resourceRequest)
     : Resource(resourceRequest, Image)
+    , m_devicePixelRatioHeaderValue(1.0)
     , m_image(0)
     , m_loadingMultipartContent(false)
+    , m_hasDevicePixelRatioHeaderValue(false)
 {
     setStatus(Unknown);
     setCustomAcceptHeader();
 }
 
 ImageResource::ImageResource(WebCore::Image* image)
     : Resource(ResourceRequest(""), Image)
     , m_image(image)
 {
     setStatus(Cached);
@@ skipping 311 matching lines @@
     Resource::error(status);
     notifyObservers();
 }
 
 void ImageResource::responseReceived(const ResourceResponse& response)
 {
     if (m_loadingMultipartContent && m_data)
         finishOnePart();
     else if (response.isMultipart())
         m_loadingMultipartContent = true;
+    if (RuntimeEnabledFeatures::clientHintsDprEnabled()) {
+        m_devicePixelRatioHeaderValue = response.httpHeaderField("DPR").toFloat(&m_hasDevicePixelRatioHeaderValue);
+        if (!m_hasDevicePixelRatioHeaderValue || m_devicePixelRatioHeaderValue <= 0.0) {
+            m_devicePixelRatioHeaderValue = 1.0;
+            m_hasDevicePixelRatioHeaderValue = false;
+        }
+    }
     Resource::responseReceived(response);
 }
 
 void ImageResource::destroyDecodedData()
 {
     bool canDeleteImage = !m_image || (m_image->hasOneRef() && m_image->isBitmapImage());
     if (isSafeToMakePurgeable() && canDeleteImage && !isLoading()) {
         // Image refs the data buffer so we should not make it purgeable while the image is alive.
         // Invoking addClient() will reconstruct the image object.
         m_image = 0;
@@ skipping 63 matching lines @@
 bool ImageResource::isAccessAllowed(SecurityOrigin* securityOrigin)
 {
     if (!image()->currentFrameHasSingleSecurityOrigin())
         return false;
     if (passesAccessControlCheck(securityOrigin))
         return true;
     return !securityOrigin->taintsCanvas(response().url());
 }
 
 } // namespace WebCore