Bug 1728414 - Remove unused ScreenReferenceSurface() function. r=aosmond

Differential Revision: https://phabricator.services.mozilla.com/D124113

gfx/thebes/gfxPlatform.cpp

@@ -915,12 +915,6 @@ void gfxPlatform::Init() {
     MOZ_CRASH("Could not initialize gfxPlatformFontList");
   }
 
-  gPlatform->mScreenReferenceSurface = gPlatform->CreateOffscreenSurface(
-      IntSize(1, 1), SurfaceFormat::A8R8G8B8_UINT32);
-  if (!gPlatform->mScreenReferenceSurface) {
-    MOZ_CRASH("Could not initialize mScreenReferenceSurface");
-  }
-
   gPlatform->mScreenReferenceDrawTarget =
       gPlatform->CreateOffscreenContentDrawTarget(IntSize(1, 1),
                                                   SurfaceFormat::B8G8R8A8);

gfx/thebes/gfxPlatform.h

@@ -627,12 +627,6 @@ class gfxPlatform : public mozilla::layers::MemoryPressureListener {
 
   static void FlushFontAndWordCaches();
 
-  /**
-   * Returns a 1x1 surface that can be used to create graphics contexts
-   * for measuring text etc as if they will be rendered to the screen
-   */
-  gfxASurface* ScreenReferenceSurface() { return mScreenReferenceSurface; }
-
   /**
    * Returns a 1x1 DrawTarget that can be used for measuring text etc. as
    * it would measure if rendered on-screen.  Guaranteed to return a