Before this patch, all ShareableBitmaps had an alpha channel. With this patch, all
ShareableBitmaps *still* have an alpha channel. But now there's a way to specify you don't
want one (which will be used in the future)!

Fixes <http://webkit.org/b/57388> Need a way to specify that a ShareableBitmap has no alpha
channel

Reviewed by Anders Carlsson.

* Shared/ShareableBitmap.cpp:
(WebKit::ShareableBitmap::Handle::Handle): Moved here from the header file, and added
initialization of m_flags.

(WebKit::ShareableBitmap::Handle::encode):
(WebKit::ShareableBitmap::Handle::decode):
Encode/decode m_flags.

(WebKit::ShareableBitmap::create):
(WebKit::ShareableBitmap::createShareable):
Pass along the new Flags argument.

(WebKit::ShareableBitmap::createHandle): Store our Flags on the Handle.
(WebKit::ShareableBitmap::ShareableBitmap): Store the Flags in m_flags.

* Shared/ShareableBitmap.h: Added Flag, Flags, and m_flags, and added a Flags argument to
some create functions.

* Shared/WebCoreArgumentCoders.cpp:
(CoreIPC::encodeImage):
* Shared/WebImage.cpp:
(WebKit::WebImage::create):
Specify that we want a bitmap that supports alpha to maintain current behavior.

* Shared/cg/ShareableBitmapCG.cpp:
(WebKit::bitmapInfo): New helper function. Includes an alpha channel only if specified in
the flags.

(WebKit::ShareableBitmap::createGraphicsContext):
(WebKit::ShareableBitmap::makeCGImage):
Use the new helper function.

* WebProcess/Plugins/Netscape/NetscapePlugin.cpp:
(WebKit::NetscapePlugin::snapshot):
* WebProcess/Plugins/PluginProxy.cpp:
(WebKit::PluginProxy::geometryDidChange):
* WebProcess/WebCoreSupport/mac/WebDragClientMac.mm:
(WebKit::convertImageToBitmap):
* WebProcess/WebCoreSupport/win/WebPopupMenuWin.cpp:
(WebKit::WebPopupMenu::setUpPlatformData):
* WebProcess/WebPage/DrawingAreaImpl.cpp:
(WebKit::DrawingAreaImpl::display):
* WebProcess/WebPage/FindController.cpp:
(WebKit::FindController::updateFindIndicator):
Specify that we want a bitmap that supports alpha to maintain current behavior.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@82442 268f45cc-cd09-0410-ab3c-d52691b4dbfc