Bug 1341009 - Add nsReflowStatus::IsEmpty() assertions to all nsIFrame::Reflow() methods and some reflow helpers, and remove unneeded Reset(). r=dholbert

nsReflowStatus::IsEmpty() assertions are added after DISPLAY_REFLOW in the
beginning of the Reflow().

A few Reflow() implementations have Reset() calls at the end which are left
in place by this patch (with an explanatory comment added to each). These
ending Reset()s are only needed for cases where a non-splittable frame
passes its own nsReflowStatus to a child's reflow method. Just in case the
child leaves a "not fully complete" value in the nsReflowStatus, the
non-splittable parent frame must clear out the nsReflowStatus before
returning, so that its own parent doesn't then try to split it.

MozReview-Commit-ID: 6Jj3jfMAqj4

layout/forms/nsNumberControlFrame.cpp

@@ -110,6 +110,7 @@ nsNumberControlFrame::Reflow(nsPresContext* aPresContext,
   MarkInReflow();
   DO_GLOBAL_REFLOW_COUNT("nsNumberControlFrame");
   DISPLAY_REFLOW(aPresContext, this, aReflowInput, aDesiredSize, aStatus);
+  MOZ_ASSERT(aStatus.IsEmpty(), "Caller should pass a fresh reflow status!");
 
   NS_ASSERTION(mOuterWrapper, "Outer wrapper div must exist!");
 
@@ -241,7 +242,7 @@ nsNumberControlFrame::Reflow(nsPresContext* aPresContext,
 
   FinishAndStoreOverflow(&aDesiredSize);
 
-  aStatus.Reset();
+  MOZ_ASSERT(aStatus.IsEmpty(), "This type of frame can't be split.");
 
   NS_FRAME_SET_TRUNCATION(aStatus, aReflowInput, aDesiredSize);
 }