Bug 1543315 - part 2: Mark VerifyIncrementalReflow() and DoVerifyReflow() as MOZ_CAN_RUN_SCRIPT_BOUNDARY r=smaug

They are debug build only methods.  So, callers of them shouldn't be marked
as `MOZ_CAN_RUN_SCRIPT` only for them.  Therefore, `MOZ_CAN_RUN_SCRIPT_BOUNDARY`
must be better.

Differential Revision: https://phabricator.services.mozilla.com/D27218

--HG--
extra : moz-landing-system : lando

layout/base/nsIPresShell.h

@@ -1774,8 +1774,8 @@ class nsIPresShell : public nsStubDocumentObserver {
       FrameMetrics::ScrollOffsetUpdateType aUpdateType);
 
 #ifdef DEBUG
-  bool VerifyIncrementalReflow();
-  void DoVerifyReflow();
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY bool VerifyIncrementalReflow();
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY void DoVerifyReflow();
   void VerifyHasDirtyRootAncestor(nsIFrame* aFrame);
   void ShowEventTargetDebug();