Bug 1364805 part 2 - Add a nsIFrame::mClass field and propagate the concrete class' value up the ctor chain. r=jfkthame

nsIFrame::mClass is of type enum class nsQueryFrame::ClassID which is
a strict subset of the nsQueryFrame::FrameIID values.  For a concrete
frame class, its FrameIID is the same numeric value as its ClassID.

MozReview-Commit-ID: 1N0AkCGo1ol

layout/forms/nsProgressFrame.cpp

@@ -38,7 +38,7 @@ NS_NewProgressFrame(nsIPresShell* aPresShell, nsStyleContext* aContext)
 NS_IMPL_FRAMEARENA_HELPERS(nsProgressFrame)
 
 nsProgressFrame::nsProgressFrame(nsStyleContext* aContext)
-  : nsContainerFrame(aContext, LayoutFrameType::Progress)
+  : nsContainerFrame(aContext, kClassID, LayoutFrameType::Progress)
   , mBarDiv(nullptr)
 {
 }