[MutationObservers] Add a document-level flag that can trivially be checked to avoid doing unnessary work if mutation observers absent
https://bugs.webkit.org/show_bug.cgi?id=74641

Patch by Rafael Weinstein <rafaelw@chromium.org> on 2011-12-15
Reviewed by Ojan Vafai.

This patch adds a byte of flags to Document, of which three bits are used to signal if any
node owned by the document has a Mutation Observer of the given type. This is used to
reduce the cost of discovering there are none to a single (inlined) method call and bit-check.
Also, a similar byte of flags which was used to optimize a particular case when mutation observers
are present has been removed, with the reasoning that we should first focus on minimizing impact on
the null-case before optimizing particular in-use cases.

Also, MutationObserverInterestGroup is broken out into its own file (which probably should have happened
earlier, but now avoids a circular header dependency).

No tests needed. This patch is just a refactor.

* CMakeLists.txt:
* GNUmakefile.list.am:
* Target.pri:
* WebCore.gypi:
* WebCore.vcproj/WebCore.vcproj:
* WebCore.xcodeproj/project.pbxproj:
* css/CSSMutableStyleDeclaration.cpp:
* dom/CharacterData.cpp:
* dom/ChildListMutationScope.cpp:
* dom/Document.cpp:
(WebCore::Document::Document):
* dom/Document.h:
(WebCore::Document::hasMutationObserversOfType):
(WebCore::Document::hasMutationObservers):
(WebCore::Document::addMutationObserverTypes):
* dom/Element.cpp:
* dom/MutationObserverInterestGroup.cpp: Added.
(WebCore::MutationObserverInterestGroup::createIfNeeded):
(WebCore::MutationObserverInterestGroup::MutationObserverInterestGroup):
(WebCore::MutationObserverInterestGroup::isOldValueRequested):
(WebCore::MutationObserverInterestGroup::enqueueMutationRecord):
* dom/MutationObserverInterestGroup.h: Copied from Source/WebCore/dom/WebKitMutationObserver.h.
(WebCore::MutationObserverInterestGroup::createForChildListMutation):
(WebCore::MutationObserverInterestGroup::createForCharacterDataMutation):
(WebCore::MutationObserverInterestGroup::createForAttributesMutation):
(WebCore::MutationObserverInterestGroup::hasOldValue):
* dom/Node.cpp:
(WebCore::Node::didMoveToNewOwnerDocument):
(WebCore::Node::getRegisteredMutationObserversOfType):
(WebCore::Node::notifyMutationObserversNodeWillDetach):
* dom/Node.h:
* dom/WebKitMutationObserver.cpp:
(WebCore::WebKitMutationObserver::observe):
* dom/WebKitMutationObserver.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@103001 268f45cc-cd09-0410-ab3c-d52691b4dbfc