Make GrTexture caching for SkPromiseImageTexture work when same texture
fulfills a different SkImage.

Bug: skia:8613
Change-Id: I7ee14112c69f8aaef223a37dda455259b501a2bf
Reviewed-on: https://skia-review.googlesource.com/c/184440
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/include/gpu/GrTexture.h b/include/gpu/GrTexture.h
index 286b7ce..80dd3f3 100644
--- a/include/gpu/GrTexture.h
+++ b/include/gpu/GrTexture.h
@@ -70,6 +70,7 @@
      */
     using IdleProc = void(void*);
     virtual void setIdleProc(IdleProc, void* context) = 0;
+    virtual void* idleContext() const = 0;
 
     /** Access methods that are only to be used within Skia code. */
     inline GrTexturePriv texturePriv();