Add GrExternalTextureData and SkCrossContextImageData

GrExternalTextureData is an API for exporting the backend-specific
information about a texture in a type-safe way, and without pointing
into the GrTexture. The new detachBackendTexture API lets us release
ownership of a texture to the client.

SkCrossContextImageData is the public API that lets clients upload
textures on one thread/GrContext, then safely transfer ownership to
another thread and GrContext for rendering.

Only GL is implemented/supported right now. Vulkan support requires
that we add thread-safe memory pools, or otherwise transfer the
actual memory block containing the texture to the new context.

Re-land of https://skia-review.googlesource.com/c/8529/

BUG=skia:

Change-Id: I48ebd57d1ea0cfd3a1db10c475f2903afb821966
Reviewed-on: https://skia-review.googlesource.com/8960
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/src/gpu/gl/GrGLTexture.h b/src/gpu/gl/GrGLTexture.h
index 029fd87a1a..16b47f1f07 100644
--- a/src/gpu/gl/GrGLTexture.h
+++ b/src/gpu/gl/GrGLTexture.h
@@ -71,6 +71,7 @@ protected:
     void onRelease() override;
     void setMemoryBacking(SkTraceMemoryDump* traceMemoryDump,
                           const SkString& dumpName) const override;
+    std::unique_ptr<GrExternalTextureData> detachBackendTexture() override;
 
 private:
     TexParams                       fTexParams;