Add osmesa to GN build.

content/shell/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/features.gni")
 import("//build/config/ui.gni")
 import("//tools/grit/grit_rule.gni")
 import("//tools/grit/repack.gni")
 if (is_android) {
   import("//build/config/android/config.gni")
@@ skipping 231 matching lines @@
 
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     cflags = [ "/wd4267" ]
   }
 
   if (is_linux) {
     configs += [ "//build/config/linux:fontconfig" ]
   }
 
   if (use_x11) {
-    # TODO(GYP) The GYP build includes a dep on the xdisplaycheck executable.
-    # Track down who added this and ask them if it's necessary, since this
-    # seems suspicious.
+    # Some tests rely on this tool at runtime. Note: it might be better if
+    # the tests that needed it had this as a dep instead of adding it here.
+    datadeps = [ "//tools/xdisplaycheck" ]
   }
 
   if (is_android) {
     #deps += [ 'content_shell_jni_headers' ]  TODO(GYP)
     #deps -= [ 'copy_test_netscape_plugin' ]  TODO(GYP)
   }
 
   if (is_posix && !is_mac && (!is_android || !is_android_webview_build)) {
     #deps += [ '../components/components.gyp:breakpad_host' ]  TODO(GYP
   }
@@ skipping 165 matching lines @@
   #  - 'LinkIncremental': '<(msvs_large_module_debug_link_mode)',
   sources = [
     "../app/startup_helper_win.cc",
     "app/shell_main.cc",
   ]
 
   deps = [
     ":content_shell_lib",
     ":pak",
     "//base/allocator",
-    #'../third_party/mesa/mesa.gyp:osmesa',  TODO(GYP)
+    "//third_party/mesa:osmesa",
   ]
 
   if (is_win) {
     deps = [ "//sandbox" ]
     if (!is_asan) {
       configs -= [ "//build/config/win:console" ]
       configs += [ "//build/config/win:windowed" ]
     }
   }
 
   if (is_mac) {
     # TODO(GYP) lots of stuff from GYP file here.
   }
 
   if (!is_android || !is_android_webview_build) {
-    deps += [
+    datadeps += [
       # NOTE: rely on host build of this target.
       #'../tools/imagediff/image_diff.gyp:image_diff',  TODO(GYP)
     ]
   }
 }
 
 } else {
   # Content shell not ready, make a dummpy to make dependency management easier.
   group("content_shell") {
   }
 }