Bug 1541398 - Force gfxImageSurface for OffscreenSurface in content r=jfkthame

For Win32k lockdown, we can't use gfxWindowsSurface in content for offscreen
surfaces, since it invokes Windows GDI calls.

It appears from testing that a gfxImageSurface works just fine, so this change
just disables the native surface usage for content processes.

Differential Revision: https://phabricator.services.mozilla.com/D70022

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

gfx/thebes/gfxWindowsPlatform.cpp

@@ -579,8 +579,11 @@ already_AddRefed<gfxASurface> gfxWindowsPlatform::CreateOffscreenSurface(
   RefPtr<gfxASurface> surf = nullptr;
 
 #ifdef CAIRO_HAS_WIN32_SURFACE
-  if (mRenderMode == RENDER_GDI || mRenderMode == RENDER_DIRECT2D)
-    surf = new gfxWindowsSurface(aSize, aFormat);
+  if (!XRE_IsContentProcess()) {
+    if (mRenderMode == RENDER_GDI || mRenderMode == RENDER_DIRECT2D) {
+      surf = new gfxWindowsSurface(aSize, aFormat);
+    }
+  }
 #endif
 
   if (!surf || surf->CairoStatus()) {