Bug 916972 - Eliminate nsIFrame::GetSplittableType() completely. r=mats,dholbert

Currently, GetSplittableType() is called only in
nsCSSFrameConstructor::CreateContinuingFrame(). The splittable concrete frames
should inherit from nsSplittableFrame, and must explicitly create continuing
frame in CreateContinuingFrame(). Thus, no need to maintain GetSplittableType().

Differential Revision: https://phabricator.services.mozilla.com/D10798

layout/generic/nsBlockFrame.cpp

@@ -404,12 +404,6 @@ NS_QUERYFRAME_HEAD(nsBlockFrame)
   NS_QUERYFRAME_ENTRY(nsBlockFrame)
 NS_QUERYFRAME_TAIL_INHERITING(nsContainerFrame)
 
-nsSplittableType
-nsBlockFrame::GetSplittableType() const
-{
-  return NS_FRAME_SPLITTABLE_NON_RECTANGULAR;
-}
-
 #ifdef DEBUG_FRAME_DUMP
 void
 nsBlockFrame::List(FILE* out, const char* aPrefix, uint32_t aFlags) const