Move GLSurfaceOSMesaX11 into it's own source file.

ui/gl/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 
 use_egl = is_win || is_android || is_linux
 use_glx = use_x11
 
@@ skipping 157 matching lines @@
       "gl_implementation_osmesa.cc",
       "gl_implementation_osmesa.h",
     ]
   }
   if (use_x11) {
     sources += [
       "gl_context_x11.cc",
       "gl_implementation_x11.cc",
       "gl_surface_egl_x11.cc",
       "gl_surface_egl_x11.h",
+      "gl_surface_osmesa_x11.cc",
+      "gl_surface_osmesa_x11.h",
       "gl_surface_x11.cc",
     ]
 
     data_deps = [
       "//third_party/angle:libEGL",
       "//third_party/angle:libGLESv2",
     ]
   }
   if (use_ozone) {
     sources += [
@@ skipping 210 matching lines @@
     sources = [
       "../android/java/src/org/chromium/ui/gl/SurfaceTextureListener.java",
       "../android/java/src/org/chromium/ui/gl/SurfaceTexturePlatformWrapper.java",
     ]
     public_deps = [
       ":surface_jni_headers",
     ]
     jni_package = "ui/gl"
   }
 }