[embedder] Ensure FlutterMetalTexture cleanup call

This ensures FlutterMetalTexture.destruction_callback gets called.

FlutterRendererConfig.get_next_drawable_callback` holds a callback used
by the embedder API to request a drawable; in the case of Metal, this
drawable is a FlutterMetalTexture.

FlutterMetalTexture.destruction_callback should be called when it's safe
to release resources associated with the FlutterMetalTexture. This
callback is not currently invoked for textures returned via
FlutterRendererConfig.get_next_drawable_callback; instead we unpack the
returned struct and pass it on.

In the compositor codepath, we do create an SkSurface that triggers the
destruction callback, here:
https://github.com/flutter/engine/blob/303e26e96561d9b76f2344e97a5fc32eb6dfdb9a/shell/platform/embedder/embedder.cc#L868-L881

Issue: flutter/flutter#116381

shell/gpu/gpu_surface_metal_delegate.h

@@ -26,9 +26,13 @@ typedef void* GPUCAMetalLayerHandle;
 // expected to be id<MTLTexture>
 typedef const void* GPUMTLTextureHandle;
 
+typedef void (*GPUMTLDestructionCallback)(void* /* destruction_context */);
+
 struct GPUMTLTextureInfo {
   int64_t texture_id;
   GPUMTLTextureHandle texture;
+  GPUMTLDestructionCallback destruction_callback;
+  void* destruction_context;
 };
 
 enum class MTLRenderTargetType { kMTLTexture, kCAMetalLayer };

shell/gpu/gpu_surface_metal_skia.mm

@@ -38,13 +38,15 @@
                                                MsaaSampleCount sample_cnt,
                                                SkColorType color_type,
                                                sk_sp<SkColorSpace> color_space,
-                                               const SkSurfaceProps* props) {
+                                               const SkSurfaceProps* props,
+                                               SkSurface::TextureReleaseProc release_proc,
+                                               SkSurface::ReleaseContext release_context) {
   GrMtlTextureInfo info;
   info.fTexture.reset([texture retain]);
   GrBackendTexture backend_texture(texture.width, texture.height, GrMipmapped::kNo, info);
-  return SkSurface::MakeFromBackendTexture(context, backend_texture, origin,
-                                           static_cast<int>(sample_cnt), color_type,
-                                           std::move(color_space), props);
+  return SkSurface::MakeFromBackendTexture(
+      context, backend_texture, origin, static_cast<int>(sample_cnt), color_type,
+      std::move(color_space), props, release_proc, release_context);
 }
 }  // namespace
 
@@ -137,7 +139,9 @@
                                                msaa_samples_,             // sample count
                                                kBGRA_8888_SkColorType,    // color type
                                                nullptr,                   // colorspace
-                                               nullptr                    // surface properties
+                                               nullptr,                   // surface properties
+                                               nullptr,                   // release proc
+                                               nullptr                    // release context
   );
 
   if (!surface) {
@@ -203,9 +207,10 @@
     return nullptr;
   }
 
-  sk_sp<SkSurface> surface =
-      CreateSurfaceFromMetalTexture(context_.get(), mtl_texture, kTopLeft_GrSurfaceOrigin,
-                                    msaa_samples_, kBGRA_8888_SkColorType, nullptr, nullptr);
+  sk_sp<SkSurface> surface = CreateSurfaceFromMetalTexture(
+      context_.get(), mtl_texture, kTopLeft_GrSurfaceOrigin, msaa_samples_, kBGRA_8888_SkColorType,
+      nullptr, nullptr, static_cast<SkSurface::TextureReleaseProc>(texture.destruction_callback),
+      texture.destruction_context);
 
   if (!surface) {
     FML_LOG(ERROR) << "Could not create the SkSurface from the metal texture.";

shell/platform/embedder/embedder.cc

@@ -477,6 +477,8 @@ InferMetalPlatformViewCreationCallback(
     FlutterMetalTexture metal_texture = ptr(user_data, &frame_info);
     texture_info.texture_id = metal_texture.texture_id;
     texture_info.texture = metal_texture.texture;
+    texture_info.destruction_callback = metal_texture.destruction_callback;
+    texture_info.destruction_context = metal_texture.user_data;
     return texture_info;
   };