Avoid parsing css text if there are identical inline style blocks.

Source/core/dom/StyleElement.cpp

Index: Source/core/dom/StyleElement.cpp
diff --git a/Source/core/dom/StyleElement.cpp b/Source/core/dom/StyleElement.cpp
index d50689a3bba2ba8cf52a76629959044db6fbaebf..4afe8edfb3454d6ece9be095c4c4c4a3e4530a53 100644
--- a/Source/core/dom/StyleElement.cpp
+++ b/Source/core/dom/StyleElement.cpp
@@ -35,6 +35,8 @@
 
 namespace WebCore {
 
+static const unsigned cacheableTextContentSizeLimit = 256;

[dglazkov, 2013/10/18 16:56:19]

How did you arrive at this number?

[tasak, 2013/10/21 12:27:37]

I have no strong reason. So I removed this magic number.

+
 static bool isCSS(Element* element, const AtomicString& type)
 {
     return type.isEmpty() || (element->isHTMLElement() ? equalIgnoringCase(type, "text/css") : (type == "text/css"));
@@ -115,6 +117,8 @@ void StyleElement::process(Element* element)
 void StyleElement::clearSheet()
 {
     ASSERT(m_sheet);
+    if (!m_sheetText.isEmpty() && m_sheet->ownerDocument() && m_sheet->ownerDocument()->isActive())

[dglazkov, 2013/10/18 16:56:19]

It might be a clearer (though more complex) factoring to introduce a switchable
block (cached vs. uncached) of machinery that deals with creating/clearing/etc.
stylesheets and using the one that's appropriate at the moment, rather than
having all these checks in the code. The switchable block solution would be a
lot less prone to code rot and accidental check omission.

[tasak, 2013/10/21 12:27:37]

I added a comments which describes the condition.

+        m_sheet->ownerDocument()->styleEngine()->unregisterStyleSheetContents(m_sheetText);
     m_sheet.release()->clearOwnerNode();
 }
 
@@ -129,6 +133,8 @@ void StyleElement::createSheet(Element* e, const String& text)
         clearSheet();
     }
 
+    m_sheetText = isHTMLStyleElement(e) && text.length() < cacheableTextContentSizeLimit ? text : String();
+
     // If type is empty or CSS, this is a CSS style sheet.
     const AtomicString& type = this->type();
     bool passesContentSecurityPolicyChecks = document.contentSecurityPolicy()->allowStyleNonce(e->fastGetAttribute(HTMLNames::nonceAttr)) || document.contentSecurityPolicy()->allowInlineStyle(e->document().url(), m_startPosition.m_line);
@@ -142,17 +148,28 @@ void StyleElement::createSheet(Element* e, const String& text)
             m_loading = true;
 
             TextPosition startPosition = m_startPosition == TextPosition::belowRangePosition() ? TextPosition::minimumPosition() : m_startPosition;
-            m_sheet = CSSStyleSheet::createInline(e, KURL(), startPosition, document.inputEncoding());
-            m_sheet->setMediaQueries(mediaQueries.release());
-            m_sheet->setTitle(e->title());
-            m_sheet->contents()->parseStringAtPosition(text, startPosition, m_createdByParser);
-
+            if (StyleSheetContents* contents = document.styleEngine()->findStyleSheetContents(m_sheetText)) {
+                // FIXME: should we use registerClient to avoid allocating a new StyleSheetContents?
+                // In this case, StyleSheetContents::singleOwnerNode() doesn't work. So need to modify
+                // codes depending on singleOwnerNode().
+                m_sheet = CSSStyleSheet::createInline(contents, e, startPosition);
+                m_sheet->setMediaQueries(mediaQueries.release());
+                m_sheet->setTitle(e->title());
+            } else {
+                m_sheet = CSSStyleSheet::createInline(e, KURL(), startPosition, document.inputEncoding());
+                m_sheet->setMediaQueries(mediaQueries.release());
+                m_sheet->setTitle(e->title());
+                m_sheet->contents()->parseStringAtPosition(text, startPosition, m_createdByParser);
+            }
             m_loading = false;
         }
     }
 
-    if (m_sheet)
+    if (m_sheet) {
         m_sheet->contents()->checkLoaded();
+        if (!m_sheetText.isEmpty() && m_sheet->contents()->isCacheable())
+            document.styleEngine()->registerStyleSheetContents(m_sheetText, m_sheet->contents());
+    }
 }
 
 bool StyleElement::isLoading() const