Add missing dependencies.

extensions/extensions_tests.gyp

 {
   'includes': [
     'extensions_tests.gypi',
   ],
   'variables': {
     # Product name is used for Mac bundle.
     'app_shell_product_name': 'App Shell',
     # The version is high enough to be supported by Omaha (at least 31)
     # but fake enough to be obviously not a Chrome release.
     'app_shell_version': '38.1234.5678.9',
@@ skipping 22 matching lines @@
         '../third_party/mojo/mojo_public.gyp:mojo_cpp_bindings',
         'common/api/api.gyp:cast_channel_proto',
         'extensions.gyp:extensions_browser',
         'extensions.gyp:extensions_common',
         'extensions.gyp:extensions_renderer',
         'extensions.gyp:extensions_shell_and_test_pak',
         'extensions.gyp:extensions_test_support',
         'extensions.gyp:extensions_utility',
         'extensions_resources.gyp:extensions_resources',
         'extensions_strings.gyp:extensions_strings',
+        # Only needed at runtime.
+        '../third_party/mesa/mesa.gyp:osmesa',
       ],
       # Needed for third_party libraries like leveldb.
       'include_dirs': [
         '..',
       ],
       'sources': [
         '<@(extensions_unittests_sources)',
       ],
       # Disable c4267 warnings until we fix size_t to int truncations.
       'msvs_disabled_warnings': [ 4267, ],
@@ skipping 22 matching lines @@
         '<(DEPTH)/components/components.gyp:guest_view_browser',
         '<(DEPTH)/components/components.gyp:guest_view_renderer',
         '<(DEPTH)/components/components.gyp:guest_view_test_support',
         '<(DEPTH)/content/content.gyp:content_app_both',
         '<(DEPTH)/content/content_shell_and_tests.gyp:content_browser_test_support',
         '<(DEPTH)/content/content_shell_and_tests.gyp:test_support_content',
         '<(DEPTH)/device/bluetooth/bluetooth.gyp:device_bluetooth_mocks',
         '<(DEPTH)/device/usb/usb.gyp:device_usb_mocks',
         '<(DEPTH)/testing/gmock.gyp:gmock',
         '<(DEPTH)/testing/gtest.gyp:gtest',
+        # Only needed at runtime.
+        '../third_party/mesa/mesa.gyp:osmesa',
       ],
       'defines': [
         'HAS_OUT_OF_PROC_TEST_RUNNER',
       ],
       'sources': [
         '<@(extensions_browsertests_sources)',
       ],
       'conditions': [
         ['OS=="win" and win_use_allocator_shim==1', {
           'dependencies': [
@@ skipping 48 matching lines @@
               'dependencies': [
                 '../tools/xdisplaycheck/xdisplaycheck.gyp:xdisplaycheck',
               ],
             }],
           ],
         }
       ],
     }],
   ],
 }