Make it possible to use OSMesa on Android

ui/gl/gl.gyp

Index: ui/gl/gl.gyp
diff --git a/ui/gl/gl.gyp b/ui/gl/gl.gyp
index 95db80957d81b3e009e91af85127ca39d6919007..ff55627f0ee7314496392b785a004c11de4f45fa 100644
--- a/ui/gl/gl.gyp
+++ b/ui/gl/gl.gyp
@@ -82,8 +82,6 @@
         'gl_implementation.cc',
         'gl_implementation.h',
         'gl_implementation_android.cc',
-        'gl_implementation_linux.cc',
-        'gl_implementation_linux.h',
         'gl_implementation_ozone.cc',
         'gl_implementation_mac.cc',
         'gl_implementation_win.cc',
@@ -193,7 +191,13 @@
           ],
           'include_dirs': [
             '<(DEPTH)/third_party/khronos',
-        ],
+          ],
+        }],
+        ['OS in ("android", "linux", "openbsd", "freebsd")', {
+          'sources': [
+            'gl_implementation_osmesa.cc',
+            'gl_implementation_osmesa.h',
+          ],
         }],
         ['use_x11 == 1', {
           'sources': [
@@ -271,7 +275,6 @@
             ],
           },
           'sources!': [
-            'gl_context_osmesa.cc',
             'system_monitor_posix.cc',
           ],
           'defines': [