Turn on seamless cubemap by default on Desktop GL for ES3.

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 7ecd8d5f47bf07b2f1410eb945e5d1295423c7b6..0e471a1835d24fb57c5a5889cf8e558b7df56fed 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -3018,6 +3018,15 @@ bool GLES2DecoderImpl::Initialize(const scoped_refptr<gfx::GLSurface>& surface,
     glEnable(GL_PROGRAM_POINT_SIZE);
   }
 
+  // ES3 requires seamless cubemap. ES2 does not.
+  // However, when ES2 is implemented on top of DX11, seamless cubemap is
+  // always enabled and there is no way to disable it.
+  // Therefore, it seems OK to also always enable it on top of Desktop GL for
+  // both ES2 and ES3 contexts.
+  if (feature_info_->gl_version_info().IsAtLeastGL(3, 2)) {
+    glEnable(GL_TEXTURE_CUBE_MAP_SEAMLESS);
+  }
+
   has_robustness_extension_ =
       context->HasExtension("GL_ARB_robustness") ||
       context->HasExtension("GL_KHR_robustness") ||