Make gtk2/gtk3 compile time switchable.

build/linux/system.gyp

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     # If any of the linux_link_FOO below are set to 1, then the corresponding
     # target will be linked against the FOO library (either dynamically or
     # statically, depending on the pkg-config files), as opposed to loading the
     # FOO library dynamically with dlopen.
@@ skipping 110 matching lines @@
                   '<!@(<(pkg-config) --libs-only-L --libs-only-other gdk-2.0)',
                 ],
                 'libraries': [
                   '<!@(<(pkg-config) --libs-only-l gdk-2.0)',
                 ],
               },
             }],
           ],
         },
         {
-          'target_name': 'gtk',
+          'target_name': 'gtk2',
           'type': 'none',
           'toolsets': ['host', 'target'],
           'variables': {
             # gtk requires gmodule, but it does not list it as a dependency
             # in some misconfigured systems.
             'gtk_packages': 'gmodule-2.0 gtk+-2.0 gthread-2.0',
           },
           'conditions': [
             ['_toolset=="target"', {
               'all_dependent_settings': {
@@ skipping 20 matching lines @@
                   '<!@(pkg-config --libs-only-L --libs-only-other <(gtk_packages))',
                 ],
                 'libraries': [
                   '<!@(pkg-config --libs-only-l <(gtk_packages))',
                 ],
               },
             }],
           ],
         },
         {
-          'target_name': 'gtkprint',
+          'target_name': 'gtkprint2',
           'type': 'none',
           'conditions': [
             ['_toolset=="target"', {
               'direct_dependent_settings': {
                 'cflags': [
                   '<!@(<(pkg-config) --cflags gtk+-unix-print-2.0)',
                 ],
               },
               'link_settings': {
                 'ldflags': [
@@ skipping 233 matching lines @@
                 ],
                 'libraries': [
                   '<!@(pkg-config --libs-only-l xtst)',
                 ],
               },
             }]
           ]
         }
       ],  # targets
     }],
+    ['use_gtk3==1', {
+      # Hide GTK3 and related dependencies when use_gtk3==0 because the user
+      # might not have the GTK3 headers yet.
+      'targets': [
+        {
+          'target_name': 'gtk3',
+          'type': 'none',
+          'toolsets': ['host', 'target'],
+          'variables': {
+            # gtk requires gmodule, but it does not list it as a dependency
+            # in some misconfigured systems.
+            'gtk_packages': 'gmodule-2.0 gtk+-3.0 gthread-2.0',
+          },
+          'conditions': [
+            ['_toolset=="target"', {
+              'all_dependent_settings': {
+                'cflags': [
+                  '<!@(<(pkg-config) --cflags <(gtk_packages))',
+                ],
+              },
+              'link_settings': {
+                'ldflags': [
+                  '<!@(<(pkg-config) --libs-only-L --libs-only-other <(gtk_packages))',
+                ],
+                'libraries': [
+                  '<!@(<(pkg-config) --libs-only-l <(gtk_packages))',
+                ],
+              },
+            }, {
+              'all_dependent_settings': {
+                'cflags': [
+                  '<!@(pkg-config --cflags <(gtk_packages))',
+                ],
+              },
+              'link_settings': {
+                'ldflags': [
+                  '<!@(pkg-config --libs-only-L --libs-only-other <(gtk_packages))',
+                ],
+                'libraries': [
+                  '<!@(pkg-config --libs-only-l <(gtk_packages))',
+                ],
+              },
+            }],
+          ],
+        },
+        {
+          'target_name': 'gtkprint3',
+          'type': 'none',
+          'conditions': [
+            ['_toolset=="target"', {
+              'direct_dependent_settings': {
+                'cflags': [
+                  '<!@(<(pkg-config) --cflags gtk+-unix-print-3.0)',
+                ],
+              },
+              'link_settings': {
+                'ldflags': [
+                  '<!@(<(pkg-config) --libs-only-L --libs-only-other gtk+-unix-print-3.0)',
+                ],
+                'libraries': [
+                  '<!@(<(pkg-config) --libs-only-l gtk+-unix-print-3.0)',
+                ],
+              },
+            }],
+          ],
+        },
+      ],
+    }],
     ['use_x11==1 and chromeos==0', {
       'targets': [
         {
           'target_name': 'xscrnsaver',
           'type': 'none',
           'direct_dependent_settings': {
             'cflags': [
               '<!@(<(pkg-config) --cflags xscrnsaver)',
             ],
           },
@@ skipping 780 matching lines @@
                   },
                 }],
               ],
             }],
           ]
         }],
       ],
     },
   ],
 }