Set the "mutable format" bit on sRGB images at creation time.

include/gpu/vk/GrVkTypes.h

 
 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrVkTypes_DEFINED
 #define GrVkTypes_DEFINED
@@ skipping 12 matching lines @@
                                                   const void* userParam);*/
 
 
 
 ///////////////////////////////////////////////////////////////////////////////
 /**
  * Types for interacting with Vulkan resources created externally to Skia. GrBackendObjects for 
  * Vulkan textures are really const GrVkImageInfo*
  */
 struct GrVkImageInfo {
+    /**
+     * If the image's format is sRGB (GrVkFormatIsSRGB returns true), then the image must have
+     * been created with VkImageCreateFlags containing VK_IMAGE_CREATE_MUTABLE_FORMAT_BIT.
+     */
     VkImage        fImage;
     VkDeviceMemory fAlloc;    // can be VK_NULL_HANDLE iff Tex is an RT and uses borrow semantics
     VkImageTiling  fImageTiling;
     VkImageLayout  fImageLayout;
     VkFormat       fFormat;
     uint32_t       fLevelCount;
 
     // This gives a way for a client to update the layout of the Image if they change the layout
     // while we're still holding onto the wrapped texture. They will first need to get a handle
     // to our internal GrVkImageInfo by calling getTextureHandle on a GrVkTexture.
     void updateImageLayout(VkImageLayout layout) { fImageLayout = layout; }
 };
 
 GR_STATIC_ASSERT(sizeof(GrBackendObject) >= sizeof(const GrVkImageInfo*));
 
 #endif