extensions: Check |enable_extensions| flag before depending on extension code.

chrome/chrome_browser_ui.gypi

Index: chrome/chrome_browser_ui.gypi
diff --git a/chrome/chrome_browser_ui.gypi b/chrome/chrome_browser_ui.gypi
index 58ee9ce4a5f9084186bd4b057371cec9b4988f55..3ffc7fadd39a6866196ab7bb7ee67cdad91fb682 100644
--- a/chrome/chrome_browser_ui.gypi
+++ b/chrome/chrome_browser_ui.gypi
@@ -2912,8 +2912,16 @@
             }],
             ['OS!="mac"', {
               'sources': [ '<@(chrome_browser_ui_views_non_mac_sources)' ],
-              'dependencies': [
-                '<(DEPTH)/extensions/components/extensions_components.gyp:native_app_window',
+              'conditions': [
+                ['enable_extensions==0', {
+                  'sources/': [
+                    ['exclude', '^browser/ui/views/extensions/'],
+                  ],
+                }, {
+                  'dependencies': [
+                    '<(DEPTH)/extensions/components/extensions_components.gyp:native_app_window',
+                  ],
+                }],
               ],
             }],
           ],