Add support for `width` based Width Client Hint

Source/core/html/parser/HTMLPreloadScanner.cpp

Index: Source/core/html/parser/HTMLPreloadScanner.cpp
diff --git a/Source/core/html/parser/HTMLPreloadScanner.cpp b/Source/core/html/parser/HTMLPreloadScanner.cpp
index d1e7e7976057d1b121a7547560d8f084cc57e31b..9fa599f8fa85bc6c2e28b532639ea76fcb840380 100644
--- a/Source/core/html/parser/HTMLPreloadScanner.cpp
+++ b/Source/core/html/parser/HTMLPreloadScanner.cpp
@@ -36,6 +36,7 @@
 #include "core/css/parser/SizesAttributeParser.h"
 #include "core/dom/Document.h"
 #include "core/frame/Settings.h"
+#include "core/html/HTMLImageElement.h"
 #include "core/html/HTMLMetaElement.h"
 #include "core/html/LinkRelAttribute.h"
 #include "core/html/parser/HTMLParserIdioms.h"
@@ -117,6 +118,9 @@ public:
         , m_sourceSize(0)
         , m_sourceSizeSet(false)
         , m_isCORSEnabled(false)
+        , m_widthValue(0)
+        , m_widthValueSet(false)
+        , m_widthPresent(false)
         , m_defer(FetchRequest::NoDefer)
         , m_allowCredentials(DoNotAllowStoredCredentials)
         , m_mediaValues(mediaValues)
@@ -180,7 +184,11 @@ public:
         if (m_sourceSizeSet && m_srcsetImageCandidate.resourceWidth() != UninitializedDescriptor) {
             resourceWidth.width = m_sourceSize;
             resourceWidth.isSet = true;
+        } else {
+            resourceWidth.isSet = m_widthValueSet;
+            resourceWidth.width = m_widthValue;

[Mike West, 2015/06/18 06:20:04]

Nit: The `if` part of the clause reverses the order of the assignment.

[Yoav Weiss, 2015/06/18 06:30:22]

I'll reverse it

         }
+
         OwnPtr<PreloadRequest> request = PreloadRequest::create(initiatorFor(m_tagImpl), position, m_urlToLoad, predictedBaseURL, resourceType(), resourceWidth, clientHintsPreferences, requestType);
         if (isCORSEnabled())
             request->setCrossOriginEnabled(allowStoredCredentials());
@@ -223,6 +231,9 @@ private:
                 m_srcsetImageCandidate = bestFitSourceForSrcsetAttribute(m_mediaValues->devicePixelRatio(), m_sourceSize, m_srcsetAttributeValue);
                 setUrlToLoad(bestFitSourceForImageAttributes(m_mediaValues->devicePixelRatio(), m_sourceSize, m_imgSrcUrl, m_srcsetImageCandidate), AllowURLReplacement);
             }
+        } else if (match(attributeName, widthAttr) && !m_widthPresent) {

[Mike West, 2015/06/18 06:20:04]

Could you drop the `widthPresent` property in favor of just checking
`m_widthValueSet` as we do with other attributes above?

[Yoav Weiss, 2015/06/18 06:30:22]

I did, but there was a bug there in cases like `<img src=foo width="500%"
width="100">`.
Once we've seen width, even if the value is not a valid one (which we ignore),
we should ignore following `width` attributes.

[Mike West, 2015/06/18 06:34:35]

Hrm. Isn't that the opposite of how the parser works? Don't we overwrite the
value of `element.width` with the final value set?

+            m_widthPresent = true;
+            m_widthValue = HTMLImageElement::widthAttributeToInt(attributeValue, m_widthValueSet);
         }
     }
 
@@ -390,6 +401,9 @@ private:
     float m_sourceSize;
     bool m_sourceSizeSet;
     bool m_isCORSEnabled;
+    int m_widthValue;
+    bool m_widthValueSet;
+    bool m_widthPresent;
     FetchRequest::DeferOption m_defer;
     StoredCredentials m_allowCredentials;
     RefPtr<MediaValues> m_mediaValues;