gfx: Use unsigned strides for gpu memory buffers.

media/renderers/mock_gpu_video_accelerator_factories.cc

Index: media/renderers/mock_gpu_video_accelerator_factories.cc
diff --git a/media/renderers/mock_gpu_video_accelerator_factories.cc b/media/renderers/mock_gpu_video_accelerator_factories.cc
index afc5d9f988cd3885afa56aae7f0596efded8ec4c..f0d5f393c12e0cd9795fa7c5fd60443b6d6359a7 100644
--- a/media/renderers/mock_gpu_video_accelerator_factories.cc
+++ b/media/renderers/mock_gpu_video_accelerator_factories.cc
@@ -52,9 +52,9 @@ class GpuMemoryBufferImpl : public gfx::GpuMemoryBuffer {
   gfx::BufferFormat GetFormat() const override {
     return format_;
   }
-  int stride(size_t plane) const override {
+  uint32_t stride(size_t plane) const override {
     DCHECK_LT(plane, num_planes_);
-    return static_cast<int>(gfx::RowSizeForBufferFormat(
+    return static_cast<uint32_t>(gfx::RowSizeForBufferFormat(
         size_.width(), format_, static_cast<int>(plane)));
   }
   gfx::GpuMemoryBufferId GetId() const override { return id_; }