Bug 1856637 - Ignore gfxDWriteFont::UpdateSystemTextVars() call if the gfxVars are not yet initialized. r=gfx-reviewers,lsalzman

Differential Revision: https://phabricator.services.mozilla.com/D190151

gfx/config/gfxVars.h

@@ -157,6 +157,12 @@ class gfxVars final {
     size_t mIndex;
   };
 
+  // Whether the gfxVars singleton instance has been initialized. Most gfx code
+  // doesn't need to check this, but code that can potentially run before
+  // gfxPlatform initialization can use this to check whether gfxVars are
+  // available yet.
+  static bool IsInitialized() { return sInstance != nullptr; }
+
  private:
   static StaticAutoPtr<gfxVars> sInstance;
   static StaticAutoPtr<nsTArray<VarBase*>> sVarList;

gfx/thebes/gfxDWriteFonts.cpp

@@ -135,6 +135,10 @@ bool gfxDWriteFont::InitDWriteSupport() {
 void gfxDWriteFont::UpdateSystemTextVars() {
   MOZ_ASSERT(XRE_IsParentProcess());
 
+  if (!gfxVars::IsInitialized()) {
+    return;
+  }
+
   BYTE newQuality = GetSystemTextQuality();
   if (gfxVars::SystemTextQuality() != newQuality) {
     gfxVars::SetSystemTextQuality(newQuality);