Update Vulkan docs

include/gpu/GrTypes.h

Index: include/gpu/GrTypes.h
diff --git a/include/gpu/GrTypes.h b/include/gpu/GrTypes.h
index 7bc949d73c366a5f19c534d5ed0e858d2147867d..6b73f3c073deb04e85f6c545ab88025d27e7e6a2 100644
--- a/include/gpu/GrTypes.h
+++ b/include/gpu/GrTypes.h
@@ -142,6 +142,7 @@ const int kBackendCount = kLast_GrBackend + 1;
 /**
  * Backend-specific 3D context handle
  *      GrGLInterface* for OpenGL. If NULL will use the default GL interface.
+ *      GrVkBackendContext* for Vulkan.
  */
 typedef intptr_t GrBackendContext;
 
@@ -569,6 +570,7 @@ struct GrBackendTextureDesc {
     /**
      * Handle to the 3D API object.
      * OpenGL: Texture ID.
+     * Vulkan: GrVkImageInfo*
      */
     GrBackendObject                 fTextureHandle;
 };
@@ -603,6 +605,7 @@ struct GrBackendRenderTargetDesc {
     /**
      * Handle to the 3D API object.
      * OpenGL: FBO ID
+     * Vulkan: GrVkImageInfo*
      */
     GrBackendObject                 fRenderTargetHandle;
 };