Support the DPR header for client hints.

Source/core/fetch/ImageResource.cpp

Index: Source/core/fetch/ImageResource.cpp
diff --git a/Source/core/fetch/ImageResource.cpp b/Source/core/fetch/ImageResource.cpp
index 90011895438217c44e913ea1e761de59110dad67..7603cbec2126e42d791717649d688cddf4527530 100644
--- a/Source/core/fetch/ImageResource.cpp
+++ b/Source/core/fetch/ImageResource.cpp
@@ -23,6 +23,7 @@
 
 #include "config.h"
 #include "core/fetch/ImageResource.h"
+#include "RuntimeEnabledFeatures.h"

[pdr., 2013/10/26 01:26:31]

Nit: Can you put this include one line lower?
...
#include "core/fetch/ImageResource.h"

#include "RuntimeEnabledFeatures.h"
#include "core/fetch/ImageResourceClient.h"
...

 
 #include "core/fetch/ImageResourceClient.h"
 #include "core/fetch/MemoryCache.h"
@@ -44,8 +45,10 @@ namespace WebCore {
 
 ImageResource::ImageResource(const ResourceRequest& resourceRequest)
     : Resource(resourceRequest, Image)
+    , m_dprHeaderValue(1.0)
     , m_image(0)
     , m_loadingMultipartContent(false)
+    , m_hasDprHeaderValue(false)
 {
     setStatus(Unknown);
     setCustomAcceptHeader();
@@ -377,6 +380,13 @@ void ImageResource::responseReceived(const ResourceResponse& response)
         finishOnePart();
     else if (response.isMultipart())
         m_loadingMultipartContent = true;
+    if (RuntimeEnabledFeatures::clientHintsDprEnabled()) {
+        m_dprHeaderValue = response.httpHeaderField("DPR").toFloat(&m_hasDprHeaderValue);
+        if (!m_hasDprHeaderValue || m_dprHeaderValue <= 0.0) {
+            m_dprHeaderValue = 1.0;
+            m_hasDprHeaderValue = false;
+        }
+    }
     Resource::responseReceived(response);
 }