Clear mutable inline style when it is empty.

Source/core/css/InlineVariablesIterator.cpp

Index: Source/core/css/InlineVariablesIterator.cpp
diff --git a/Source/platform/graphics/filters/SourceAlpha.h b/Source/core/css/InlineVariablesIterator.cpp
similarity index 53%
copy from Source/platform/graphics/filters/SourceAlpha.h
copy to Source/core/css/InlineVariablesIterator.cpp
index 519a31af32f9ccd11cac8787250ec4660b7e9754..5b2c56f19734bc166b85c01b3f6e6c4492a4925e 100644
--- a/Source/platform/graphics/filters/SourceAlpha.h
+++ b/Source/core/css/InlineVariablesIterator.cpp
@@ -1,5 +1,4 @@
 /*
- * Copyright (C) 2009 Dirk Schulze <krit@webkit.org>
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
@@ -18,35 +17,35 @@
  * Boston, MA 02110-1301, USA.
  */
 
-#ifndef SourceAlpha_h
-#define SourceAlpha_h
+#include "config.h"
+#include "core/css/InlineVariablesIterator.h"
 
-#include "platform/graphics/filters/Filter.h"
-#include "platform/graphics/filters/FilterEffect.h"
+#include "RuntimeEnabledFeatures.h"
+#include "core/css/CSSVariableValue.h"
+#include "core/css/StylePropertySet.h"
+#include "core/dom/Element.h"
 
 namespace WebCore {
 
-class PLATFORM_EXPORT SourceAlpha : public FilterEffect {
-public:
-    static PassRefPtr<SourceAlpha> create(Filter*);
+InlineVariablesIterator::InlineVariablesIterator(Element* element)
+    : m_element(element)
+{
+    ASSERT(RuntimeEnabledFeatures::cssVariablesEnabled());
 
-    static const AtomicString& effectName();
-
-    virtual void determineAbsolutePaintRect();
-
-    virtual FilterEffectType filterEffectType() const { return FilterEffectTypeSourceInput; }
-
-    virtual TextStream& externalRepresentation(TextStream&, int indention) const;
-
-private:
-    SourceAlpha(Filter* filter)
-        : FilterEffect(filter)
-    {
+    const StylePropertySet* propertySet = element->inlineStyle();
+    if (propertySet) {
+        initRemainingNames(propertySet);
     }
+}
 
-    virtual void applySoftware() OVERRIDE;
-};
+PassRefPtr<InlineVariablesIterator> InlineVariablesIterator::create(Element* element)
+{
+    return adoptRef(new InlineVariablesIterator(element));
+}
 
-} // namespace WebCore
+MutableStylePropertySet* InlineVariablesIterator::propertySet() const
+{
+    return m_element->ensureMutableInlineStyle();
+}
 
-#endif // SourceAlpha_h
+} // namespace WebCore