Revert of Finish OSMesa support for Ozone X11.

ui/gl/BUILD.gn

Index: ui/gl/BUILD.gn
diff --git a/ui/gl/BUILD.gn b/ui/gl/BUILD.gn
index 0dd5f6fc0a7bdf1e36c50fa8ba8a95438a0d22f5..183df6572d11a4ad430de409a9063252760df460 100644
--- a/ui/gl/BUILD.gn
+++ b/ui/gl/BUILD.gn
@@ -14,7 +14,7 @@
 }
 
 use_egl = is_win || is_android || is_linux
-build_x11_gl = use_x11 || ozone_platform_x11
+use_glx = use_x11 || ozone_platform_x11
 
 if (is_android) {
   import("//build/config/android/config.gni")
@@ -28,7 +28,7 @@
 
 config("gl_config") {
   defines = []
-  if (build_x11_gl) {
+  if (use_glx) {
     defines += [
       "GL_GLEXT_PROTOTYPES",
       "USE_GLX",
@@ -189,6 +189,8 @@
       "gl_surface_egl_x11.h",
       "gl_surface_glx_x11.cc",
       "gl_surface_glx_x11.h",
+      "gl_surface_osmesa_x11.cc",
+      "gl_surface_osmesa_x11.h",
     ]
 
     deps += [ "//ui/base/x" ]
@@ -198,7 +200,7 @@
       "//third_party/angle:libGLESv2",
     ]
   }
-  if (build_x11_gl) {
+  if (use_glx) {
     sources += [
       "gl_bindings_autogen_glx.cc",
       "gl_bindings_autogen_glx.h",
@@ -210,8 +212,6 @@
       "gl_image_glx.h",
       "gl_surface_glx.cc",
       "gl_surface_glx.h",
-      "gl_surface_osmesa_x11.cc",
-      "gl_surface_osmesa_x11.h",
       "gl_visual_picker_glx.cc",
       "gl_visual_picker_glx.h",
     ]
@@ -383,7 +383,7 @@
     ]
   }
 
-  if (build_x11_gl) {
+  if (use_glx) {
     sources += [ "glx_api_unittest.cc" ]
   }