Prepare texture for cross context usage when using the Metal backend.

This implementation will only work when the two contexts are created using
the same device and command queue. This restriction is now applied in Flutter.
With the patch and context setup, async texture uploads on the IO thread are
functional.

Change-Id: I887d24b2612cde933e088f74f33912a3a8762159
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/275758
Commit-Queue: Chinmay Garde <[email protected]>
Commit-Queue: Greg Daniel <[email protected]>
Auto-Submit: Chinmay Garde <[email protected]>
Reviewed-by: Greg Daniel <[email protected]>

Author: chinmaygarde

src/gpu/mtl/GrMtlGpu.h

@@ -100,9 +100,7 @@ class GrMtlGpu : public GrGpu {
     void insertSemaphore(GrSemaphore* semaphore) override;
     void waitSemaphore(GrSemaphore* semaphore) override;
     void checkFinishProcs() override;
-    std::unique_ptr<GrSemaphore> prepareTextureForCrossContextUsage(GrTexture*) override {
-        return nullptr;
-    }
+    std::unique_ptr<GrSemaphore> prepareTextureForCrossContextUsage(GrTexture*) override;
 
     // When the Metal backend actually uses indirect command buffers, this function will actually do
     // what it says. For now, every command is encoded directly into the primary command buffer, so

src/gpu/mtl/GrMtlGpu.mm

@@ -226,6 +226,11 @@ static bool get_feature_set(id<MTLDevice> device, MTLFeatureSet* featureSet) {
     }
 }
 
+std::unique_ptr<GrSemaphore> GrMtlGpu::prepareTextureForCrossContextUsage(GrTexture*) {
+    submitCommandBuffer(SyncQueue::kSkip_SyncQueue);
+    return nullptr;
+}
+
 sk_sp<GrGpuBuffer> GrMtlGpu::onCreateBuffer(size_t size, GrGpuBufferType type,
                                             GrAccessPattern accessPattern, const void* data) {
     return GrMtlBuffer::Make(this, size, type, accessPattern, data);