fix unsigned/signed warning on linux for GrVkDescriptorPool::numPoolSizes()

src/gpu/vk/GrVkDescriptorPool.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 GrVkDescriptorPool_DEFINED
 #define GrVkDescriptorPool_DEFINED
 
 #include "GrVkResource.h"
 
 #include "vulkan/vulkan.h"
 
 class GrVkGpu;
 
 class GrVkDescriptorPool : public GrVkResource {
 public:
     class DescriptorTypeCounts {
     public:
         DescriptorTypeCounts() {
             memset(fDescriptorTypeCount, 0, sizeof(fDescriptorTypeCount));
         }
 
         void setTypeCount(VkDescriptorType type, uint8_t count);
-        uint32_t numPoolSizes() const;
+        int numPoolSizes() const;
 
         // Determines if for each i, that.fDescriptorTypeCount[i] <= fDescriptorTypeCount[i];
         bool isSuperSet(const DescriptorTypeCounts& that) const;
     private:
         uint8_t fDescriptorTypeCount[VK_DESCRIPTOR_TYPE_RANGE_SIZE];
 
         friend class GrVkDescriptorPool;
     };
 
     explicit GrVkDescriptorPool(const GrVkGpu* gpu, const DescriptorTypeCounts& typeCounts);
 
     VkDescriptorPool descPool() const { return fDescPool; }
 
     void reset(const GrVkGpu* gpu);
 
     // Returns whether or not this descriptor pool could be used, assuming it gets fully reset and
     // not in use by another draw, to support the requested typeCounts.
     bool isCompatible(const DescriptorTypeCounts& typeCounts) const;
 
 private:
     void freeGPUData(const GrVkGpu* gpu) const override;
 
     DescriptorTypeCounts fTypeCounts;
     VkDescriptorPool     fDescPool;
 
     typedef GrVkResource INHERITED;
 };
 
-
-#endif
+#endif