gyp: add osmesa target to factor out common code

gyp/gputest.gyp

 # Copyright 2015 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 {
   'targets': [
     {
       'target_name': 'skgputest',
       'product_name': 'skia_skgputest',
       'type': 'static_library',
@@ skipping 14 matching lines @@
           '../tools/gpu',
         ],
       },
       'dependencies': [
         'skia_lib.gyp:skia_lib',
       ],
       'sources': [
         '<!@(python find.py ../tools/gpu "*")'
       ],
       'conditions': [
-        [ 'skia_mesa and skia_os == "linux"', {
-          'link_settings': {
-            'libraries': [
-              '-lOSMesa',
-            ],
-          },
-        }],
-        [ 'skia_mesa and skia_os == "mac"', {
-          'link_settings': {
-            'libraries': [
-              '/opt/X11/lib/libOSMesa.dylib',
-            ],
-          },
-          'include_dirs': [
-             '/opt/X11/include/',
-          ],
-        }],
+        [ 'skia_mesa', { 'dependencies': [ 'osmesa' ] } ],
         [ 'skia_angle', {
           'dependencies': [
             'angle.gyp:*',
           ],
           'export_dependent_settings': [
             'angle.gyp:*',
           ],
         }],
         [ '(skia_os == "linux" or skia_os == "chromeos") and skia_egl == 1', {
           'link_settings': {
@@ skipping 52 matching lines @@
         [ 'skia_angle == 0', {
           'sources/': [
             ['exclude', '_angle\.(h|cpp)$'],
           ],
         }],
         [ 'skia_command_buffer == 0', {
           'sources/': [ ['exclude', '_command_buffer\.(h|cpp)$'], ],
         }],
       ],
     },
+    {
+      'target_name': 'osmesa',
+      'type': 'none',
+      'direct_dependent_settings': {
+        'link_settings': { 'libraries': [ '-lOSMesa', ], },
+        'conditions': [
+          [ 'skia_os == "mac"', {
+            'link_settings': { 'library_dirs' : [ '/opt/X11/lib' ], },
+            'include_dirs': [ '/opt/X11/include', ],
+          }],
+        ],
+      },
+    },
   ],
 }