[Impeller] force render pass construction on all backends to ensure image layout is transitioned/render pass state setup. (#50539)

Fixes flutter/flutter#142358

We rely on the render pass encoding to transition image textures from undefined to shader read layout. If an empty pass is created with no clear color, we still need to create the pass on the Vulkan backend.

Author: Jonah Williams

impeller/aiks/aiks_unittests.cc

@@ -503,6 +503,28 @@ TEST_P(AiksTest, CanPictureConvertToImage) {
   ASSERT_TRUE(OpenPlaygroundHere(canvas.EndRecordingAsPicture()));
 }
 
+// Regression test for https://github.com/flutter/flutter/issues/142358 .
+// Without a change to force render pass construction the image is left in an
+// undefined layout and triggers a validation error.
+TEST_P(AiksTest, CanEmptyPictureConvertToImage) {
+  Canvas recorder_canvas;
+
+  Canvas canvas;
+  AiksContext renderer(GetContext(), nullptr);
+  Paint paint;
+  paint.color = Color::BlackTransparent();
+  canvas.DrawPaint(paint);
+  Picture picture = recorder_canvas.EndRecordingAsPicture();
+  auto image = picture.ToImage(renderer, ISize{1000, 1000});
+  if (image) {
+    canvas.DrawImage(image, Point(), Paint());
+    paint.color = Color{0.1, 0.1, 0.1, 0.2};
+    canvas.DrawRect(Rect::MakeSize(ISize{1000, 1000}), paint);
+  }
+
+  ASSERT_TRUE(OpenPlaygroundHere(canvas.EndRecordingAsPicture()));
+}
+
 TEST_P(AiksTest, BlendModeShouldCoverWholeScreen) {
   Canvas canvas;
   Paint paint;

impeller/entity/entity_pass.cc

@@ -901,9 +901,10 @@ bool EntityPass::OnRender(
   }
   auto clear_color_size = pass_target.GetRenderTarget().GetRenderTargetSize();
 
-  if (!collapsed_parent_pass && GetClearColor(clear_color_size).has_value()) {
-    // Force the pass context to create at least one new pass if the clear color
-    // is present.
+  if (!collapsed_parent_pass) {
+    // Always force the pass to construct the render pass object, even if there
+    // is not a clear color. This ensures that the attachment textures are
+    // cleared/transitioned to the right state.
     pass_context.GetRenderPass(pass_depth);
   }