Bug 1375299 (part 1) - Reduce usage of MOZ_GECKO_PROFILER. r=mstange.

This patch reduces the differences between builds where the profiler is enabled
and those where the profiler is disabled. It does this by removing numerous
MOZ_GECKO_PROFILER checks.

These changes have the following consequences.

- Various functions and classes are now defined in all builds, and so can be
  used unconditionally: profiler_add_marker(), profiler_set_js_context(),
  profiler_clear_js_context(), profiler_get_pseudo_stack(), AutoProfilerLabel.
  (They are effectively no-ops in non-profiler builds, of course.)

- The no-op versions of PROFILER_* are now gone. The remaining versions are
  almost no-ops when the profiler isn't built.

xpcom/base/CycleCollectedJSRuntime.cpp

@@ -930,19 +930,19 @@ CycleCollectedJSRuntime::GCNurseryCollectionCallback(JSContext* aContext,
     timelines->AddMarkerForAllObservedDocShells(abstractMarker);
   }
 
-#ifdef MOZ_GECKO_PROFILER
   if (aProgress == JS::GCNurseryProgress::GC_NURSERY_COLLECTION_START) {
     self->mLatestNurseryCollectionStart = TimeStamp::Now();
   } else if ((aProgress == JS::GCNurseryProgress::GC_NURSERY_COLLECTION_END) &&
              profiler_is_active())
   {
+#ifdef MOZ_GECKO_PROFILER
     PROFILER_MARKER_PAYLOAD(
       "GCMinor",
       MakeUnique<GCMinorMarkerPayload>(self->mLatestNurseryCollectionStart,
                                        TimeStamp::Now(),
                                        JS::MinorGcToJSON(aContext)));
-  }
 #endif
+  }
 
   if (self->mPrevGCNurseryCollectionCallback) {
     self->mPrevGCNurseryCollectionCallback(aContext, aProgress, aReason);