Make HTMLMediaElement destructor not to dispatch load event

This patch changes HTMLMediaElement destructor not to dispatch load event to make JavaScript load event handler in stable state, e.g. accessing destructing media elements in event handler.

Original crash bug is occurred in EditorClientImpl::clearUndoRedoOperations(), which is called recursively during undo stack destruction. The first call of  EditorClientImpl::clearUndoRedoOperations() is kicked by removing IFRAME via HTMLFrameOwnerElement::OwnerElement(). Second call is kicked by destructing HTMLMediaElement in undo stack via ResourceFetcher::didLoadResource() in media player, associated to HTMLMediaElement, destruction.

BUG=275223
TEST=LayoutTests/editing/undo/audio-in-undo-stack-crash.html

Review URL: https://chromiumcodereview.appspot.com/23555002

git-svn-id: svn://svn.chromium.org/blink/trunk@157865 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Prevent crash in DocumentLoader::dataReceived

This patch prevents a crash in DocumentLoader::dataReceived where the
frame can be destructed in the middle of dataReceived.

BUG=

Review URL: https://chromiumcodereview.appspot.com/23781008

git-svn-id: svn://svn.chromium.org/blink/trunk@157866 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add toRenderSVGResourceRadialGradient() fuction, and use it.

This function has type checking assertions for helping to find bad-cast bugs.

BUG=N/A

Review URL: https://chromiumcodereview.appspot.com/23766034

git-svn-id: svn://svn.chromium.org/blink/trunk@157867 bbb929c8-8fbe-4397-9dbb-9b2b20218538