Bug 1458556: Upgrade an assertion to try get a crash earlier and (hopefully) a reproducible test-case. r=xidorn

MozReview-Commit-ID: 2UT7M2KhHRf

layout/base/RestyleManager.cpp

@@ -2592,7 +2592,8 @@ RestyleManager::ProcessPostTraversal(
   nsIFrame* styleFrame = nsLayoutUtils::GetStyleFrame(aElement);
   nsIFrame* primaryFrame = aElement->GetPrimaryFrame();
 
-  MOZ_ASSERT(aElement->HasServoData(), "How in the world?");
+  MOZ_DIAGNOSTIC_ASSERT(aElement->HasServoData(),
+                        "Element without Servo data on a post-traversal? How?");
 
   // NOTE(emilio): This is needed because for table frames the bit is set on the
   // table wrapper (which is the primary frame), not on the table itself.