unit_tests: Fix link error (missing libXi) on Linux

build/linux/system.gyp

 # Copyright (c) 2009 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.
 
 {
   'conditions': [
     ['sysroot!=""', {
       'variables': {
         'pkg-config': './pkg-config-wrapper "<(sysroot)"',
       },
@@ skipping 216 matching lines @@
           },
       }],
       # When XInput2 is available (i.e. inputproto version is 2.0), the
       # pkg-config command will succeed, so the output will be empty.
       ['"<!@(<(pkg-config) --atleast-version=2.0 inputproto || echo $?)"==""', {
         'direct_dependent_settings': {
           'defines': [
             'HAVE_XINPUT2',
           ],
         },
+        'link_settings': {
+          'ldflags': [
+            '<!@(<(pkg-config) --libs-only-L --libs-only-other xi)',
+          ],
+          'libraries': [
+            '<!@(<(pkg-config) --libs-only-l xi)',
+          ],
+        }
       }],
       ],
     },
     {
       'target_name': 'xext',
       'type': 'settings',
       'conditions': [
         ['_toolset=="target"', {
           'direct_dependent_settings': {
             'cflags': [
@@ skipping 111 matching lines @@
       ],
     },
   ],
 }
 
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