touchui: First pass at XInput2 message pump.

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 207 matching lines @@
             ],
           },
           'link_settings': {
             'ldflags': [
               '<!@(<(pkg-config) --libs-only-L --libs-only-other x11)',
             ],
             'libraries': [
               '<!@(<(pkg-config) --libs-only-l x11)',
             ],
           },
-      }]]
+      }],
+      # 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',
+          ],
+        },
+      }],
+      ],
     },
     {
       'target_name': 'xext',
       'type': 'settings',
       'conditions': [
         ['_toolset=="target"', {
           'direct_dependent_settings': {
             'cflags': [
               '<!@(<(pkg-config) --cflags xext)',
             ],
@@ skipping 109 matching lines @@
       ],
     },
   ],
 }
 
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