gpu: support immutable texture on Linux Mesa driver and GLES3.

cc/test/test_web_graphics_context_3d.h

Index: cc/test/test_web_graphics_context_3d.h
diff --git a/cc/test/test_web_graphics_context_3d.h b/cc/test/test_web_graphics_context_3d.h
index a7d5e0b6eb1fa3c9226d739e950a4b1e8d0a58e0..e33c07a196055874bd3efaca151b900db541db0e 100644
--- a/cc/test/test_web_graphics_context_3d.h
+++ b/cc/test/test_web_graphics_context_3d.h
@@ -304,6 +304,9 @@ class TestWebGraphicsContext3D {
   void set_support_compressed_texture_etc1(bool support) {
     test_capabilities_.gpu.texture_format_etc1 = support;
   }
+  void set_support_texture_format_bgra8888(bool support) {
+    test_capabilities_.gpu.texture_format_bgra8888 = support;
+  }
   void set_support_texture_storage(bool support) {
     test_capabilities_.gpu.texture_storage = support;
   }