ozone: Constify members of gbm_wrapper::{Buffer,Device}

No functional change.

Change-Id: I98bb99a0df8e7eecec323252c17cfbfd46861bf2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1637228
Auto-Submit: Michael Spang <spang@chromium.org>
Commit-Queue: Daniel Nicoara <dnicoara@chromium.org>
Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Cr-Commit-Position: refs/heads/master@{#665295}

ui/ozone/common/linux/gbm_wrapper.cc

@@ -175,16 +175,16 @@ class Buffer final : public ui::GbmBuffer {
     buffer->mmap_data_ = nullptr;
   }
 
-  gbm_bo* bo_ = nullptr;
+  gbm_bo* const bo_;
   void* mmap_data_ = nullptr;
 
-  uint32_t format_ = 0;
-  uint64_t format_modifier_ = 0;
-  uint32_t flags_ = 0;
+  const uint32_t format_;
+  const uint64_t format_modifier_;
+  const uint32_t flags_;
 
-  gfx::Size size_;
+  const gfx::Size size_;
 
-  gfx::NativePixmapHandle handle_;
+  const gfx::NativePixmapHandle handle_;
 
   DISALLOW_COPY_AND_ASSIGN(Buffer);
 };
@@ -304,7 +304,7 @@ class Device final : public ui::GbmDevice {
   }
 
  private:
-  gbm_device* device_;
+  gbm_device* const device_;
 
   DISALLOW_COPY_AND_ASSIGN(Device);
 };