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

Source/core/dom/StyleEngine.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 34 matching lines @@
 #include "core/page/Page.h"
 #include "core/page/PageGroup.h"
 #include "core/page/Settings.h"
 #include "core/svg/SVGStyleElement.h"
 #include "platform/URLPatternMatcher.h"
 
 namespace WebCore {
 
 using namespace HTMLNames;
 
+
+static HashMap<AtomicString, StyleSheetContents*>& textToSheetCache()
+{
+    typedef HashMap<AtomicString, StyleSheetContents*> TextToSheetCache;

[esprehn, 2013/11/15 10:27:37]

No need for the typedefs since they're inside functions.

[tasak, 2014/01/09 09:24:50]

I tried "DEFINE_STATIC_LOCAL((HashMap<...>), ..)". So I saw:
../../third_party/WebKit/Source/core/dom/StyleEngine.cpp:58:5: error: expected
primary-expression before 'static'
../../third_party/WebKit/Source/core/dom/StyleEngine.cpp:58:5: error: expected
';' before 'static'

Looking at other codes, they use typedef.

+    DEFINE_STATIC_LOCAL(TextToSheetCache, cache, ());
+    return cache;
+}
+
+static HashMap<StyleSheetContents*, AtomicString>& sheetToTextCache()
+{
+    typedef HashMap<StyleSheetContents*, AtomicString> SheetToTextCache;

[esprehn, 2013/11/15 10:27:37]

Ditto.

+    DEFINE_STATIC_LOCAL(SheetToTextCache, cache, ());
+    return cache;
+}
+
 StyleEngine::StyleEngine(Document& document)
     : m_document(document)
     , m_pendingStylesheets(0)
     , m_injectedStyleSheetCacheValid(false)
     , m_needsUpdateActiveStylesheetsOnStyleRecalc(false)
     , m_documentStyleSheetCollection(document)
     , m_needsDocumentStyleSheetsUpdate(true)
     , m_usesSiblingRules(false)
     , m_usesSiblingRulesOverride(false)
     , m_usesFirstLineRules(false)
@@ skipping 344 matching lines @@
     for (TreeScopeSet::iterator it = begin; it != end; ++it) {
         if (StyleSheetCollection* collection = m_styleSheetCollectionMap.get(*it)) {
             styleResolver->setBuildScopedStyleTreeInDocumentOrder(!collection->scopingNodesForStyleScoped());
             styleResolver->appendAuthorStyleSheets(0, collection->activeAuthorStyleSheets());
         }
     }
     styleResolver->finishAppendAuthorStyleSheets();
     styleResolver->setBuildScopedStyleTreeInDocumentOrder(false);
 }
 
+PassRefPtr<CSSStyleSheet> StyleEngine::createSheet(Element* e, const String& text, TextPosition startPosition, bool createdByParser)
+{
+    AtomicString textContent(text);
+
+    HashMap<AtomicString, StyleSheetContents*>::AddResult result = textToSheetCache().add(textContent, 0);
+
+    e->document().styleEngine()->addPendingSheet();
+
+    RefPtr<CSSStyleSheet> styleSheet;
+    if (result.isNewEntry || !result.iterator->value) {
+        styleSheet = CSSStyleSheet::createInline(e, KURL(), startPosition, e->document().inputEncoding());
+        styleSheet->contents()->parseStringAtPosition(text, startPosition, createdByParser);
+
+        if (result.isNewEntry && styleSheet->contents()->maybeCacheable()) {
+            result.iterator->value = styleSheet->contents();
+            sheetToTextCache().add(styleSheet->contents(), textContent);
+        }
+    } else {
+        ASSERT(result.iterator->value->maybeCacheable());
+        styleSheet = CSSStyleSheet::createInline(result.iterator->value, e, startPosition);
+    }
+
+    ASSERT(styleSheet);
+    styleSheet->setTitle(e->title());
+
+    return styleSheet;
 }
+
+void StyleEngine::removeSheet(StyleSheetContents* contents)
+{
+    HashMap<StyleSheetContents*, AtomicString>::iterator it = sheetToTextCache().find(contents);
+    if (it == sheetToTextCache().end())
+        return;
+
+    textToSheetCache().remove(it->value);
+    sheetToTextCache().remove(contents);
+}
+
+void StyleEngine::clearSheetCache()
+{
+    textToSheetCache().clear();
+    sheetToTextCache().clear();

[esprehn, 2013/11/15 10:27:37]

Should not be needed. This is bad too, you're clearing the cache for _all_
documents not just this one so unloading an iframe would nuke the cache across
the whole process.

[tasak, 2014/01/09 09:24:50]

I'm still using this method when compatibility mode is changed.

+}
+
+}