gfx: Use unsigned strides for gpu memory buffers.

components/display_compositor/buffer_queue_unittest.cc

Index: components/display_compositor/buffer_queue_unittest.cc
diff --git a/components/display_compositor/buffer_queue_unittest.cc b/components/display_compositor/buffer_queue_unittest.cc
index 17ef79b0a8c3ccf4815ea7187d6e67d880a74ccd..52121a2c1d2dccca282c6b703a6e84c47731d2f3 100644
--- a/components/display_compositor/buffer_queue_unittest.cc
+++ b/components/display_compositor/buffer_queue_unittest.cc
@@ -41,7 +41,7 @@ class StubGpuMemoryBufferImpl : public gfx::GpuMemoryBuffer {
   gfx::BufferFormat GetFormat() const override {
     return gfx::BufferFormat::BGRX_8888;
   }
-  int stride(size_t plane) const override { return 0; }
+  uint32_t stride(size_t plane) const override { return 0u; }
   gfx::GpuMemoryBufferId GetId() const override {
     return gfx::GpuMemoryBufferId(0);
   }