Bug 1354255 - Remove ElementRestyler::ComputeStyleChangeFor profiler instrumentation due to overhead. r=Ehsan

This only has overhead if the profiler is running, but it means that it has
the potential to skew restyle times in profiles.
We haven't measured the overhead of this, but it's probably non-zero, and at
the moment our profiling efforts are more focused on getting accurate times
than on getting useful information about restyling cost sources.

MozReview-Commit-ID: 3KmiiyGrxZH

--HG--
extra : rebase_source : df7047f1af5f36f7a1b3a18498d8eb5508ee0b93

layout/base/GeckoRestyleManager.cpp

@@ -3055,15 +3055,10 @@ ElementRestyler::ComputeStyleChangeFor(nsIFrame*          aFrame,
                                        nsTArray<RefPtr<nsStyleContext>>&
                                          aSwappedStructOwners)
 {
-  nsIContent* content = aFrame->GetContent();
-  std::string elemDesc;
-  if (profiler_is_active() && content) {
-    elemDesc = ToString(*content);
-  }
+  PROFILER_LABEL("ElementRestyler", "ComputeStyleChangeFor",
+                 js::ProfileEntry::Category::CSS);
 
-  PROFILER_LABEL_DYNAMIC("ElementRestyler", "ComputeStyleChangeFor",
-                         js::ProfileEntry::Category::CSS,
-                         content ? elemDesc.c_str() : "<unknown>");
+  nsIContent* content = aFrame->GetContent();
   if (aMinChange) {
     aChangeList->AppendChange(aFrame, content, aMinChange);
   }