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 100 matching lines @@
       ]
     },
   ],
   'conditions': [
     ['test_isolation_mode != "noop"', {
       'targets': [
         {
           'target_name': 'extensions_browsertests_run',
           'type': 'none',
           'dependencies': [
+            '../third_party/mesa/mesa.gyp:osmesa',
             'extensions_browsertests',
           ],
           'includes': [
             '../build/isolate.gypi',
           ],
           'sources': [
             'extensions_browsertests.isolate',
           ],
         },
         {
           'target_name': 'extensions_unittests_run',
           'type': 'none',
           'dependencies': [
+            '../third_party/mesa/mesa.gyp:osmesa',
             'extensions_unittests',
           ],
           'includes': [
             '../build/isolate.gypi',
           ],
           'sources': [
             'extensions_unittests.isolate',
           ],
           'conditions': [
             ['use_x11 == 1', {
               'dependencies': [
                 '../tools/xdisplaycheck/xdisplaycheck.gyp:xdisplaycheck',
               ],
             }],
           ],
         }
       ],
     }],
   ],
 }