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 6a6037c85f0ca3a36eec38648178e60bb09e0cfa..97605624bb69348ae9f5835469ea371489b4d05e 100644
--- a/Source/core/dom/StyleElement.cpp
+++ b/Source/core/dom/StyleElement.cpp
@@ -35,6 +35,8 @@
 
 namespace WebCore {
 
+static const unsigned cacheableTextContentSizeLimit = (unsigned)-1; // UNLIMITED
+
 static bool isCSS(Element* element, const AtomicString& type)
 {
     return type.isEmpty() || (element->isHTMLElement() ? equalIgnoringCase(type, "text/css") : (type == "text/css"));
@@ -115,7 +117,12 @@ void StyleElement::process(Element* element)
 void StyleElement::clearSheet()
 {
     ASSERT(m_sheet);
+    // If the sheet was cached one(=!m_sheetText.isEmpty()), the cached sheet has an owner document and
+    // document is not destroyed (not in ~Document), we need to unregister.
+    if (!m_sheetText.isEmpty() && m_sheet->ownerDocument() && m_sheet->ownerDocument()->isActive())
+        m_sheet->ownerDocument()->styleEngine()->unregisterStyleSheetContents(m_sheetText);
     m_sheet.release()->clearOwnerNode();
+    m_sheetText = AtomicString();
 }
 
 void StyleElement::createSheet(Element* e, const String& text)
@@ -129,6 +136,9 @@ void StyleElement::createSheet(Element* e, const String& text)
         clearSheet();
     }
 
+    ASSERT(!isHTMLStyleElement(e) || m_sheetText.isEmpty());
+    AtomicString sheetText = isHTMLStyleElement(e) ? AtomicString(text.impl()) : AtomicString();
+
     // 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 +152,30 @@ 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(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->copy(), 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 (!sheetText.isEmpty() && m_sheet->contents()->isCacheable()) {
+            m_sheetText = sheetText;
+            document.styleEngine()->registerStyleSheetContents(m_sheetText, m_sheet->contents());
+        }
+    }
 }
 
 bool StyleElement::isLoading() const