[Windows] Address #36422 by adding a context for async resource uploading

shell/platform/windows/angle_surface_manager.cc

@@ -126,13 +126,37 @@ bool AngleSurfaceManager::Initialize() {
     return false;
   }
 
+  egl_resource_context_ = eglCreateContext(
+      egl_display_, egl_config_, egl_context_, display_context_attributes);
+
+  if (egl_resource_context_ == EGL_NO_CONTEXT) {
+    OutputDebugString(L"EGL: Failed to create EGL resource context");
+    return false;
+  }
+
   return true;
 }
 
 void AngleSurfaceManager::CleanUp() {
+  EGLBoolean result = EGL_FALSE;
+
   if (egl_display_ != EGL_NO_DISPLAY && egl_context_ != EGL_NO_CONTEXT) {
-    eglDestroyContext(egl_display_, egl_context_);
+    result = eglDestroyContext(egl_display_, egl_context_);
     egl_context_ = EGL_NO_CONTEXT;
+
+    if (result == EGL_FALSE) {
+      OutputDebugString(L"EGL: Failed to destroy context");
+    }
+  }
+
+  if (egl_display_ != EGL_NO_DISPLAY &&
+      egl_resource_context_ != EGL_NO_CONTEXT) {
+    result = eglDestroyContext(egl_display_, egl_resource_context_);
+    egl_resource_context_ = EGL_NO_CONTEXT;
+
+    if (result == EGL_FALSE) {
+      OutputDebugString(L"EGL: Failed to destroy resource context");
+    }
   }
 
   if (egl_display_ != EGL_NO_DISPLAY) {
@@ -184,6 +208,11 @@ bool AngleSurfaceManager::MakeCurrent(const EGLSurface surface) {
           EGL_TRUE);
 }
 
+bool AngleSurfaceManager::MakeResourceCurrent() {
+  return (eglMakeCurrent(egl_display_, EGL_NO_SURFACE, EGL_NO_SURFACE,
+                         egl_resource_context_) == EGL_TRUE);
+}
+
 EGLBoolean AngleSurfaceManager::SwapBuffers(const EGLSurface surface) {
   return (eglSwapBuffers(egl_display_, surface));
 }

shell/platform/windows/angle_surface_manager.h

@@ -46,6 +46,10 @@ class AngleSurfaceManager {
   // surfaces returning a boolean result reflecting success.
   bool MakeCurrent(const EGLSurface surface);
 
+  // Binds egl_resource_context_ to the current rendering thread and to the draw
+  // and read surfaces returning a boolean result reflecting success.
+  bool MakeResourceCurrent();
+
   // Swaps the front and back buffers of the DX11 swapchain backing surface if
   // not null.
   EGLBoolean SwapBuffers(const EGLSurface surface);
@@ -55,13 +59,17 @@ class AngleSurfaceManager {
   void CleanUp();
 
  private:
-  // EGL representation of native display
+  // EGL representation of native display.
   EGLDisplay egl_display_;
 
-  // EGL representation of current rendering context
+  // EGL representation of current rendering context.
   EGLContext egl_context_;
 
-  // current frame buffer configuration
+  // EGL representation of current rendering context used for async texture
+  // uploads.
+  EGLContext egl_resource_context_;
+
+  // current frame buffer configuration.
   EGLConfig egl_config_;
 
   // State representing success or failure of display initialization used when

shell/platform/windows/flutter_windows.cc

@@ -69,6 +69,10 @@ static FLUTTER_API_SYMBOL(FlutterEngine)
                                        const char* what) -> void* {
     return eglGetProcAddress(what);
   };
+  config.open_gl.make_resource_current = [](void* user_data) -> bool {
+    auto host = static_cast<flutter::Win32FlutterWindow*>(user_data);
+    return host->MakeResourceCurrent();
+  };
 
   FlutterProjectArgs args = {};
   args.struct_size = sizeof(FlutterProjectArgs);

shell/platform/windows/win32_flutter_window.cc

@@ -279,6 +279,10 @@ bool Win32FlutterWindow::MakeCurrent() {
   return surface_manager->MakeCurrent(render_surface);
 }
 
+bool Win32FlutterWindow::MakeResourceCurrent() {
+  return surface_manager->MakeResourceCurrent();
+}
+
 bool Win32FlutterWindow::ClearContext() {
   return surface_manager->MakeCurrent(nullptr);
 }

shell/platform/windows/win32_flutter_window.h

@@ -85,6 +85,7 @@ class Win32FlutterWindow : public Win32Window {
   // Callbacks for clearing context, settings context and swapping buffers.
   bool ClearContext();
   bool MakeCurrent();
+  bool MakeResourceCurrent();
   bool SwapBuffers();
 
   // Sends a window metrics update to the Flutter engine using current window