Fix gcc warnings in Vulkan backend

src/gpu/vk/GrVkGpu.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrVkGpu.h"
 
 #include "GrContextOptions.h"
@@ skipping 265 matching lines @@
                                       VK_IMAGE_LAYOUT_GENERAL,
                                       srcAccessMask,
                                       dstAccessMask,
                                       srcStageMask,
                                       dstStageMask,
                                       false);
             }
             success = this->uploadTexDataLinear(vkTex, left, top, width, height, config,
                                                 texels.begin()->fPixels, texels.begin()->fRowBytes);
         } else {
-            uint32_t mipLevels = texels.count();
+            int mipLevels = texels.count();
             if (vkTex->texturePriv().maxMipMapLevel() != mipLevels) {
                 if (!vkTex->reallocForMipmap(this, mipLevels)) {
                     return false;
                 }
             }
             success = this->uploadTexDataOptimal(vkTex, left, top, width, height, config, texels);
         }
     }
     
     return success;
@@ skipping 155 matching lines @@
             memcpy(dst, src, trimRowBytes * currentHeight);
         } else {
             SkRectMemcpy(dst, trimRowBytes, src, rowBytes, trimRowBytes, currentHeight);
         }
 
         VkBufferImageCopy& region = regions.push_back();
         memset(&region, 0, sizeof(VkBufferImageCopy));
         region.bufferOffset = individualMipOffsets[currentMipLevel];
         region.bufferRowLength = currentWidth;
         region.bufferImageHeight = currentHeight;
-        region.imageSubresource = { VK_IMAGE_ASPECT_COLOR_BIT, currentMipLevel, 0, 1 };
+        region.imageSubresource = { VK_IMAGE_ASPECT_COLOR_BIT, SkToU32(currentMipLevel), 0, 1 };
         region.imageOffset = { left, top, 0 };
         region.imageExtent = { (uint32_t)currentWidth, (uint32_t)currentHeight, 1 };
     }
 
     transferBuffer->unmap();
 
     // make sure the unmap has finished
     transferBuffer->addMemoryBarrier(this,
                                      VK_ACCESS_HOST_WRITE_BIT,
                                      VK_ACCESS_TRANSFER_READ_BIT,
@@ skipping 1321 matching lines @@
     aglSwapBuffers(aglGetCurrentContext());
     int set_a_break_pt_here = 9;
     aglSwapBuffers(aglGetCurrentContext());
 #elif defined(SK_BUILD_FOR_WIN32)
     SwapBuf();
     int set_a_break_pt_here = 9;
     SwapBuf();
 #endif
 #endif
 }