Add support for the object-position CSS property.

Source/core/css/Pair.h

Index: Source/core/css/Pair.h
diff --git a/Source/core/css/Pair.h b/Source/core/css/Pair.h
index b4446b3d823832031f5b3ca7f199a62d9c8c8267..2c1940f0b5267cd1b4aeda31a481b5c1360edd85 100644
--- a/Source/core/css/Pair.h
+++ b/Source/core/css/Pair.h
@@ -34,52 +34,69 @@ namespace WebCore {
 // it (eliminating some extra -webkit- internal properties).
 class Pair : public RefCounted<Pair> {
 public:
+    enum IdenticalValuesPolicy { DropIdenticalValues, KeepIdenticalValues };
+
     static PassRefPtr<Pair> create()
     {
         return adoptRef(new Pair);
     }
-    static PassRefPtr<Pair> create(PassRefPtr<CSSPrimitiveValue> first, PassRefPtr<CSSPrimitiveValue> second)
+    static PassRefPtr<Pair> create(PassRefPtr<CSSPrimitiveValue> first, PassRefPtr<CSSPrimitiveValue> second, IdenticalValuesPolicy identicalValuesPolicy)
     {
-        return adoptRef(new Pair(first, second));
+        return adoptRef(new Pair(first, second, identicalValuesPolicy));
     }
     virtual ~Pair() { }
 
     CSSPrimitiveValue* first() const { return m_first.get(); }
     CSSPrimitiveValue* second() const { return m_second.get(); }
+    IdenticalValuesPolicy identicalValuesPolicy() const { return m_identicalValuesPolicy; }
 
     void setFirst(PassRefPtr<CSSPrimitiveValue> first) { m_first = first; }
     void setSecond(PassRefPtr<CSSPrimitiveValue> second) { m_second = second; }
+    void setIdenticalValuesPolicy(IdenticalValuesPolicy identicalValuesPolicy) { m_identicalValuesPolicy = identicalValuesPolicy; }
 
     String cssText() const
     {
-
-        return generateCSSString(first()->cssText(), second()->cssText());
+        return generateCSSString(first()->cssText(), second()->cssText(), m_identicalValuesPolicy);
     }
 
-    bool equals(const Pair& other) const { return compareCSSValuePtr(m_first, other.m_first) && compareCSSValuePtr(m_second, other.m_second); }
+    bool equals(const Pair& other) const
+    {
+        return compareCSSValuePtr(m_first, other.m_first)
+            && compareCSSValuePtr(m_second, other.m_second)
+            && m_identicalValuesPolicy == other.m_identicalValuesPolicy;
+    }
 
     String serializeResolvingVariables(const HashMap<AtomicString, String>& variables) const
     {
-        return generateCSSString(first()->customSerializeResolvingVariables(variables),
-                                 second()->customSerializeResolvingVariables(variables));
+        return generateCSSString(
+            first()->customSerializeResolvingVariables(variables),
+            second()->customSerializeResolvingVariables(variables),
+            m_identicalValuesPolicy);
     }
 
     bool hasVariableReference() const { return first()->hasVariableReference() || second()->hasVariableReference(); }
 
 private:
-    Pair() : m_first(0), m_second(0) { }
-    Pair(PassRefPtr<CSSPrimitiveValue> first, PassRefPtr<CSSPrimitiveValue> second)
-        : m_first(first), m_second(second) { }
+    Pair()
+        : m_first(0)
+        , m_second(0)
+        , m_identicalValuesPolicy(DropIdenticalValues) { }

[pdr., 2013/08/27 20:07:19]

This will be expensive for other users of Pair. Is there a better way to handle
this?

[mstensho (USE GERRIT), 2013/08/27 20:23:11]

What if I subclass Pair and do my stuff there and add another value to the
CSSPrimitiveValue::UnitTypes enum?

[mstensho (USE GERRIT), 2013/08/29 13:09:31]

If the memory usage increase in Pair is a concern, we don't HAVE to store a
Pair's identical-values policy inside Pair objects (although I believe that's
where it belongs, if we want to follow basic principles of good object-oriented
design, but I also do realize that might not be the main concern right here).

Rather than storing this information in Pair, we could store it inside CSSValue;
either (A) use one available bit there, or (B) use two UnitTypes for Pair. Today
we have CSS_PAIR. It could be split into CSS_PAIR_DROP_IDENTICAL_VALUES and
CSS_PAIR_KEEP_IDENTICAL_VALUES.

None of these approaches would cause any immediate memory usage increase, but
both, perhaps especially the latter, feel a bit weird/silly to me. Both would
require some custom plumbing when it comes to creating a CSSPrimitiveValue from
the parser, since we can no longer simply pass a Pair object, since we also need
to supply the Pair's identical-values policy along with it.

No matter what we choose to do, a CSS pair value needs to know one way or
another if it should collapse/drop identical values or not, in order to
serialize itself properly.

+
+    Pair(PassRefPtr<CSSPrimitiveValue> first, PassRefPtr<CSSPrimitiveValue> second, IdenticalValuesPolicy identicalValuesPolicy)
+        : m_first(first)
+        , m_second(second)
+        , m_identicalValuesPolicy(identicalValuesPolicy) { }
 
-    static String generateCSSString(const String& first, const String& second)
+    static String generateCSSString(const String& first, const String& second, IdenticalValuesPolicy identicalValuesPolicy)
     {
-        if (first == second)
+        if (identicalValuesPolicy == DropIdenticalValues && first == second)
             return first;
         return first + ' ' + second;
     }
 
     RefPtr<CSSPrimitiveValue> m_first;
     RefPtr<CSSPrimitiveValue> m_second;
+    IdenticalValuesPolicy m_identicalValuesPolicy;
 };
 
 } // namespace