Bug 1519918 - Make nsFontFaceLoader::mFontFaceSet a weak reference. r=heycam

And start tracking the loader ASAP to be on the safe side.

Both sides already take care of cleaning up pointers on destruction.

Differential Revision: https://phabricator.services.mozilla.com/D16514

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

layout/style/FontFaceSet.cpp

@@ -581,6 +581,7 @@ nsresult FontFaceSet::StartLoad(gfxUserFontEntry* aUserFontEntry,
 
   RefPtr<nsFontFaceLoader> fontLoader = new nsFontFaceLoader(
       aUserFontEntry, aFontFaceSrc->mURI->get(), this, channel);
+  mLoaders.PutEntry(fontLoader);
 
   if (LOG_ENABLED()) {
     LOG(
@@ -638,7 +639,6 @@ nsresult FontFaceSet::StartLoad(gfxUserFontEntry* aUserFontEntry,
   }
 
   if (NS_SUCCEEDED(rv)) {
-    mLoaders.PutEntry(fontLoader);
     fontLoader->StartedLoading(streamLoader);
     // let the font entry remember the loader, in case we need to cancel it
     aUserFontEntry->SetLoader(fontLoader);

layout/style/nsFontFaceLoader.h

@@ -55,7 +55,8 @@ class nsFontFaceLoader final : public nsIStreamLoaderObserver,
  private:
   RefPtr<gfxUserFontEntry> mUserFontEntry;
   nsCOMPtr<nsIURI> mFontURI;
-  RefPtr<mozilla::dom::FontFaceSet> mFontFaceSet;
+  // Cleared in FontFaceSet::~FontFaceSet, and on cancelation and such too.
+  mozilla::dom::FontFaceSet* MOZ_NON_OWNING_REF mFontFaceSet;
   nsCOMPtr<nsIChannel> mChannel;
   nsCOMPtr<nsITimer> mLoadTimer;
   mozilla::TimeStamp mStartTime;