Ensure that Layer::AutoSaveLayer objects are not immediately destructed (#6264)

Fixes https://github.com/flutter/flutter/issues/20859

flow/layers/backdrop_filter_layer.cc

@@ -16,8 +16,9 @@ void BackdropFilterLayer::Paint(PaintContext& context) const {
   TRACE_EVENT0("flutter", "BackdropFilterLayer::Paint");
   FML_DCHECK(needs_painting());
 
-  Layer::AutoSaveLayer(context, SkCanvas::SaveLayerRec{&paint_bounds(), nullptr,
-                                                       filter_.get(), 0});
+  Layer::AutoSaveLayer save = Layer::AutoSaveLayer::Create(
+      context,
+      SkCanvas::SaveLayerRec{&paint_bounds(), nullptr, filter_.get(), 0});
   PaintChildren(context);
 }
 

flow/layers/color_filter_layer.cc

@@ -19,7 +19,8 @@ void ColorFilterLayer::Paint(PaintContext& context) const {
   SkPaint paint;
   paint.setColorFilter(std::move(color_filter));
 
-  Layer::AutoSaveLayer(context, paint_bounds(), &paint);
+  Layer::AutoSaveLayer save =
+      Layer::AutoSaveLayer::Create(context, paint_bounds(), &paint);
   PaintChildren(context);
 }
 

flow/layers/layer.cc

@@ -35,6 +35,19 @@ Layer::AutoSaveLayer::AutoSaveLayer(const PaintContext& paint_context,
   paint_context_.canvas.saveLayer(layer_rec);
 }
 
+Layer::AutoSaveLayer Layer::AutoSaveLayer::Create(
+    const PaintContext& paint_context,
+    const SkRect& bounds,
+    const SkPaint* paint) {
+  return Layer::AutoSaveLayer(paint_context, bounds, paint);
+}
+
+Layer::AutoSaveLayer Layer::AutoSaveLayer::Create(
+    const PaintContext& paint_context,
+    const SkCanvas::SaveLayerRec& layer_rec) {
+  return Layer::AutoSaveLayer(paint_context, layer_rec);
+}
+
 Layer::AutoSaveLayer::~AutoSaveLayer() {
   if (paint_context_.checkerboard_offscreen_layers) {
     DrawCheckerboard(&paint_context_.canvas, bounds_);

flow/layers/layer.h

@@ -12,6 +12,7 @@
 #include "flutter/flow/raster_cache.h"
 #include "flutter/flow/texture.h"
 #include "flutter/fml/build_config.h"
+#include "flutter/fml/compiler_specific.h"
 #include "flutter/fml/logging.h"
 #include "flutter/fml/macros.h"
 #include "flutter/fml/trace_event.h"
@@ -67,6 +68,18 @@ class Layer {
   // draws a checkerboard over the layer if that is enabled in the PaintContext.
   class AutoSaveLayer {
    public:
+    FML_WARN_UNUSED_RESULT static AutoSaveLayer Create(
+        const PaintContext& paint_context,
+        const SkRect& bounds,
+        const SkPaint* paint);
+
+    FML_WARN_UNUSED_RESULT static AutoSaveLayer Create(
+        const PaintContext& paint_context,
+        const SkCanvas::SaveLayerRec& layer_rec);
+
+    ~AutoSaveLayer();
+
+   private:
     AutoSaveLayer(const PaintContext& paint_context,
                   const SkRect& bounds,
                   const SkPaint* paint);
@@ -74,9 +87,6 @@ class Layer {
     AutoSaveLayer(const PaintContext& paint_context,
                   const SkCanvas::SaveLayerRec& layer_rec);
 
-    ~AutoSaveLayer();
-
-   private:
     const PaintContext& paint_context_;
     const SkRect bounds_;
   };

flow/layers/opacity_layer.cc

@@ -17,7 +17,8 @@ void OpacityLayer::Paint(PaintContext& context) const {
   SkPaint paint;
   paint.setAlpha(alpha_);
 
-  Layer::AutoSaveLayer save(context, paint_bounds(), &paint);
+  Layer::AutoSaveLayer save =
+      Layer::AutoSaveLayer::Create(context, paint_bounds(), &paint);
   PaintChildren(context);
 }
 

flow/layers/shader_mask_layer.cc

@@ -14,7 +14,8 @@ void ShaderMaskLayer::Paint(PaintContext& context) const {
   TRACE_EVENT0("flutter", "ShaderMaskLayer::Paint");
   FML_DCHECK(needs_painting());
 
-  Layer::AutoSaveLayer(context, paint_bounds(), nullptr);
+  Layer::AutoSaveLayer save =
+      Layer::AutoSaveLayer::Create(context, paint_bounds(), nullptr);
   PaintChildren(context);
 
   SkPaint paint;