[//gpu][mac] Support multiple concurrent read access in Graphite

We have discovered that the lack of this support is a source of
significant overhead for Graphite vs. Ganesh on at least one perf
benchmark, as this is supported in Ganesh [2].

This function was added here [2]. It's not obvious to me what the
requirements are for it being able to be supported in a given
representation. This CL enables it for
SkiaGraphiteDawnImageRepresentation for Mac. Local testing shows that
it works unproblematically, including on YouTube and WebGPU's demo
pages.

[1] https://source.chromium.org/chromium/chromium/src/+/main:gpu/command_buffer/service/shared_image/iosurface_image_backing.mm;l=373-375;drc=b58207f5aecc39db7d3da766e7d171e5d2c3598e;bpv=1;bpt=1
[2] https://chromium-review.googlesource.com/c/chromium/src/+/1963098

Change-Id: Ie6c182baf69897dd3f8358883cd83489ff3b573b
Bug: 1523517
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5250233
Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1260328}

gpu/command_buffer/service/shared_image/iosurface_image_backing.mm

@@ -753,6 +753,7 @@ class IOSurfaceImageBacking::DawnRepresentation final
 
   wgpu::Texture BeginAccess(wgpu::TextureUsage usage) final;
   void EndAccess() final;
+  bool SupportsMultipleConcurrentReadAccess() final;
 
  private:
   static constexpr wgpu::TextureUsage kReadOnlyUsage =
@@ -897,6 +898,11 @@ void IOSurfaceImageBacking::DawnRepresentation::EndAccess() {
 }
 #endif  // BUILDFLAG(USE_DAWN)
 
+bool IOSurfaceImageBacking::DawnRepresentation::
+    SupportsMultipleConcurrentReadAccess() {
+  return true;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 // IOSurfaceImageBacking
 

gpu/command_buffer/service/shared_image/shared_image_representation.cc

@@ -835,6 +835,10 @@ wgpu::Texture DawnImageRepresentation::BeginAccess(
   return this->BeginAccess(usage);
 }
 
+bool DawnImageRepresentation::SupportsMultipleConcurrentReadAccess() {
+  return false;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 // SharedImageRepresentationFactoryRef
 

gpu/command_buffer/service/shared_image/shared_image_representation.h

@@ -779,6 +779,8 @@ class GPU_GLES2_EXPORT DawnImageRepresentation
       AllowUnclearedAccess allow_uncleared,
       const gfx::Rect& update_rect);
 
+  virtual bool SupportsMultipleConcurrentReadAccess();
+
  private:
   friend class WrappedDawnCompoundImageRepresentation;
 

gpu/command_buffer/service/shared_image/skia_graphite_dawn_image_representation.cc

@@ -226,4 +226,9 @@ void SkiaGraphiteDawnImageRepresentation::EndReadAccess() {
   mode_ = RepresentationAccessMode::kNone;
 }
 
+bool SkiaGraphiteDawnImageRepresentation::
+    SupportsMultipleConcurrentReadAccess() {
+  return dawn_representation_->SupportsMultipleConcurrentReadAccess();
+}
+
 }  // namespace gpu

gpu/command_buffer/service/shared_image/skia_graphite_dawn_image_representation.h

@@ -36,6 +36,7 @@ class GPU_GLES2_EXPORT SkiaGraphiteDawnImageRepresentation
 
   std::vector<skgpu::graphite::BackendTexture> BeginReadAccess() override;
   void EndReadAccess() override;
+  bool SupportsMultipleConcurrentReadAccess() override;
 
  private:
   SkiaGraphiteDawnImageRepresentation(