Refactor DragData class to use PlatformStrategies in the Mac implementation.

Refactor DragData class to use PlatformStrategies in the Mac implementation.
https://bugs.webkit.org/show_bug.cgi?id=78768

Reviewed by Darin Adler.

Source/WebCore:

No new tests. No behavior change.

* WebCore.exp.in: Added new exported method of the PlatformPasteboard class.
* platform/DragData.h:
(WebCore::DragData::pasteboardName): Added pasteboardName and removed pasteboard.
* platform/PasteboardStrategy.h: Added color() method.
* platform/PlatformPasteboard.h: Ditto.
* platform/mac/ClipboardMac.mm:
(WebCore::Clipboard::create): Changed to use pasteboardName() method.
* platform/mac/DragDataMac.mm: All the methods below have been changed to use pasteboardName
and the pasteboardStrategy() methods.
(WebCore::DragData::DragData):
(WebCore::DragData::canSmartReplace):
(WebCore::DragData::containsColor):
(WebCore::DragData::containsFiles):
(WebCore::DragData::numberOfFiles):
(WebCore::DragData::asFilenames):
(WebCore::DragData::containsPlainText):
(WebCore::DragData::asPlainText):
(WebCore::DragData::asColor):
(WebCore::DragData::containsCompatibleContent):
(WebCore::DragData::asURL):
(WebCore::DragData::asFragment):
* platform/mac/PlatformPasteboardMac.mm:
(WebCore::PlatformPasteboard::color): Added implementation of the color() method.

Source/WebKit/mac:

* WebCoreSupport/WebPlatformStrategies.h: Added color() method.
* WebCoreSupport/WebPlatformStrategies.mm:
(WebPlatformStrategies::color):

Source/WebKit2:

* WebProcess/WebCoreSupport/WebPlatformStrategies.cpp: Added color() method.
(WebKit::WebPlatformStrategies::color):
* WebProcess/WebCoreSupport/WebPlatformStrategies.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@108101 268f45cc-cd09-0410-ab3c-d52691b4dbfc