Enable srcset support in HTMLImageElement

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 0b51791a374d39388adc0e23565c850647be29e6..bf719c6972d2dc5b172f116bee41884cb2030fd0 100644
--- a/Source/core/html/parser/HTMLPreloadScanner.cpp
+++ b/Source/core/html/parser/HTMLPreloadScanner.cpp
@@ -29,6 +29,7 @@
 #include "core/html/parser/HTMLPreloadScanner.h"
 
 #include "HTMLNames.h"
+#include "RuntimeEnabledFeatures.h"
 #include "core/html/InputTypeNames.h"
 #include "core/html/LinkRelAttribute.h"
 #include "core/html/parser/HTMLParserIdioms.h"
@@ -90,10 +91,11 @@ static String initiatorFor(const StringImpl* tagImpl)
 
 class TokenPreloadScanner::StartTagScanner {
 public:
-    explicit StartTagScanner(const StringImpl* tagImpl)
+    explicit StartTagScanner(const StringImpl* tagImpl, float deviceScaleFactor = 1.0)

[abarth-chromium, 2013/09/13 05:54:07]

Please remove the default argument.  All callers should be forced to supply a
device scale factor.

         : m_tagImpl(tagImpl)
         , m_linkIsStyleSheet(false)
         , m_inputIsImage(false)
+        , m_deviceScaleFactor(deviceScaleFactor)
     {
         if (!match(m_tagImpl, imgTag)
             && !match(m_tagImpl, inputTag)
@@ -102,6 +104,14 @@ public:
             m_tagImpl = 0;
     }
 
+    void applySrcset()
+    {
+        // Resolve between src and srcSet if we have them.
+        if (RuntimeEnabledFeatures::srcsetEnabled() && !m_srcSetAttribute.isEmpty()) {

[ojan, 2013/09/12 23:26:38]

Nit: single line if should not have curly braces.

+            setUrlToLoad(bestFitSourceForImageAttributes(m_deviceScaleFactor, m_urlToLoad, m_srcSetAttribute), true);

[abarth-chromium, 2013/09/13 05:54:07]

This line of code isn't correct.  You haven't distinguished between srcset on
images and srcset on other elements, which means you're preloading srcset for
iframes as well.  Please add a test for this case.

+        }
+    }
+
     void processAttributes(const HTMLToken::AttributeList& attributes)
     {
         ASSERT(isMainThread());
@@ -112,6 +122,8 @@ public:
             String attributeValue = StringImpl::create8BitIfPossible(iter->value);
             processAttribute(attributeName, attributeValue);
         }
+
+        applySrcset();

[abarth-chromium, 2013/09/13 05:54:07]

Instead of doing the after every tag, we should only do it when it could
possibly matter, specifically when m_tagImpl matches imgTag.  Please don't just
add a branch here for m_tagImpl.  We already take that branch in
processAttribute.  We don't want to take it twice.

[Yoav Weiss, 2013/09/13 10:04:18]

Assuming m_srcSetAttribute is only initialized for images, is going into
applySrcset() and doing nothing there acceptable? 

I prefer to keep a single if statement inside the function and call it twice.
Alternatively, I can simply inline applySrcset()'s content in both calls.

[abarth-chromium, 2013/09/13 17:58:12]

The important thing is to only do srcset-specific work for imgTags.  Here you're
doing srcset-specific work for all tags.

     }
 
     void processAttributes(const Vector<CompactHTMLToken::Attribute>& attributes)
@@ -120,6 +132,8 @@ public:
             return;
         for (Vector<CompactHTMLToken::Attribute>::const_iterator iter = attributes.begin(); iter != attributes.end(); ++iter)
             processAttribute(iter->name, iter->value);
+
+        applySrcset();
     }
 
     PassOwnPtr<PreloadRequest> createPreloadRequest(const KURL& predictedBaseURL, const SegmentedString& source)
@@ -168,13 +182,16 @@ private:
         return rel.isStyleSheet() && !rel.isAlternate() && rel.iconType() == InvalidIcon && !rel.isDNSPrefetch();
     }
 
-    void setUrlToLoad(const String& attributeValue)
+    void setUrlToLoad(const String& value, bool allowReplacement = false)

[abarth-chromium, 2013/09/13 05:54:07]

Please remove the default value for the last argument and use an enum instead of
a boolean so that callers can see what the second argument means.

     {
         // We only respect the first src/href, per HTML5:
         // http://www.whatwg.org/specs/web-apps/current-work/multipage/tokenization.html#attribute-name-state
-        if (!m_urlToLoad.isEmpty())
+        if (!allowReplacement && !m_urlToLoad.isEmpty())
+            return;
+        String url = stripLeadingAndTrailingHTMLSpaces(value);
+        if (url.isEmpty())
             return;
-        m_urlToLoad = stripLeadingAndTrailingHTMLSpaces(attributeValue);
+        m_urlToLoad = url;
     }
 
     const String& charset() const
@@ -215,16 +232,19 @@ private:
 
     const StringImpl* m_tagImpl;
     String m_urlToLoad;
+    String m_srcSetAttribute;

[abarth-chromium, 2013/09/13 05:54:07]

Where did you ever assign this member?

Please add a test that verifies that preloading works correctly.

[Yoav Weiss, 2013/09/13 10:04:18]

That is a bug (assignment lost in merge). Thanks!

     String m_charset;
     String m_crossOriginMode;
     bool m_linkIsStyleSheet;
     String m_mediaAttribute;
     bool m_inputIsImage;
+    float m_deviceScaleFactor;
 };
 
-TokenPreloadScanner::TokenPreloadScanner(const KURL& documentURL)
+TokenPreloadScanner::TokenPreloadScanner(const KURL& documentURL, float deviceScaleFactor)
     : m_documentURL(documentURL)
     , m_inStyle(false)
+    , m_deviceScaleFactor(deviceScaleFactor)
     , m_templateCount(0)
 {
 }
@@ -305,7 +325,7 @@ void TokenPreloadScanner::scanCommon(const Token& token, const SegmentedString&
             return;
         }
 
-        StartTagScanner scanner(tagImpl);
+        StartTagScanner scanner(tagImpl, m_deviceScaleFactor);
         scanner.processAttributes(token.attributes());
         OwnPtr<PreloadRequest> request = scanner.createPreloadRequest(m_predictedBaseElementURL, source);
         if (request)
@@ -326,8 +346,8 @@ void TokenPreloadScanner::updatePredictedBaseURL(const Token& token)
         m_predictedBaseElementURL = KURL(m_documentURL, stripLeadingAndTrailingHTMLSpaces(hrefAttribute->value)).copy();
 }
 
-HTMLPreloadScanner::HTMLPreloadScanner(const HTMLParserOptions& options, const KURL& documentURL)
-    : m_scanner(documentURL)
+HTMLPreloadScanner::HTMLPreloadScanner(const HTMLParserOptions& options, const KURL& documentURL, float deviceScaleFactor)
+    : m_scanner(documentURL, deviceScaleFactor)
     , m_tokenizer(HTMLTokenizer::create(options))
 {
 }