Don't convert back and forth between weak ptr

Author: bdero

impeller/renderer/backend/metal/surface_mtl.h

@@ -43,10 +43,10 @@ class SurfaceMTL final : public Surface {
   id<MTLDrawable> drawable() const { return drawable_; }
 
  private:
-  std::weak_ptr<Context> context_;
+  std::shared_ptr<Context> context_;
   id<MTLDrawable> drawable_ = nil;
 
-  SurfaceMTL(const std::weak_ptr<Context>& context,
+  SurfaceMTL(const std::shared_ptr<Context>& context,
              const RenderTarget& target,
              id<MTLDrawable> drawable);
 

impeller/renderer/backend/metal/surface_mtl.mm

@@ -112,11 +112,11 @@
   render_target_desc.SetStencilAttachment(stencil0);
 
   // The constructor is private. So make_unique may not be used.
-  return std::unique_ptr<SurfaceMTL>(new SurfaceMTL(
-      context->weak_from_this(), render_target_desc, current_drawable));
+  return std::unique_ptr<SurfaceMTL>(
+      new SurfaceMTL(context, render_target_desc, current_drawable));
 }
 
-SurfaceMTL::SurfaceMTL(const std::weak_ptr<Context>& context,
+SurfaceMTL::SurfaceMTL(const std::shared_ptr<Context>& context,
                        const RenderTarget& target,
                        id<MTLDrawable> drawable)
     : Surface(target), context_(context), drawable_(drawable) {}
@@ -131,7 +131,7 @@
   }
 
   id<MTLCommandBuffer> command_buffer =
-      ContextMTL::Cast(context_.lock().get())->CreateMTLCommandBuffer();
+      ContextMTL::Cast(context_.get())->CreateMTLCommandBuffer();
   [command_buffer presentDrawable:drawable_];
   [command_buffer commit];