Add a data_dep for osmesa to //ui/gl and run ui_unittests.

third_party/mesa/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")
 if (is_posix) {
   import("//build/config/gcc/gcc_version.gni")
 }
 
 config("mesa_headers_config") {
@@ skipping 636 matching lines @@
     ":mesa_headers",
   ]
 }
 
 if (!is_android) {  # TODO(GYP) enable for Android.
   # Building this target will hide the native OpenGL shared library and
   # replace it with a slow software renderer.
   # TODO(GYP) http://crbug.com/380327 need support for loadable_module.
   #loadable_module("osmesa") {
   shared_library("osmesa") {
+    # Make sure this only gets used in tests.
+    testonly = true
+
     sources = [
       "src/src/mesa/drivers/common/driverfuncs.c",
       "src/src/mesa/drivers/common/driverfuncs.h",
       "src/src/mesa/drivers/common/meta.c",
       "src/src/mesa/drivers/common/meta.h",
       "src/src/mesa/drivers/osmesa/osmesa.c",
       "src/src/mesa/drivers/osmesa/osmesa.def",
     ]
 
     configs -= [ "//build/config/compiler:chromium_code" ]
     configs += [
       ":mesa_headers_config",
       "//build/config/compiler:no_chromium_code",
     ]
     previous_configs = configs
     configs = []
     configs = [ ":mesa_internal_config" ] + previous_configs
 
     include_dirs = [ "src/src/mesa/drivers" ]
 
     if (is_clang) {
       # Mesa triggers some of these Clang warnings.
       configs -= [ "//build/config/clang:extra_warnings" ]
     }
 
     deps = [
+      ":mesa",
       ":mesa_headers",
-      ":mesa",
       ":mesa_libglslcommon",
     ]
 
     if (is_win) {
       defines = [
         "BUILD_GL32",
         "KEYWORD1=GLAPI",
         "KEYWORD2=GLAPIENTRY",
       ]
     }
   }
 } else {
   #  Placeholder to allow targets to unconditionally depend on this.
   group("osmesa") {
   }
 }  # !is_android
 # TODO(GYP) Android osmesa_in_lib_dir target.