Default enable the Blink GC plugin.

Source/config.gyp

 #
 # Copyright (C) 2013 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
@@ skipping 14 matching lines @@
 # DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #
 {
   'variables': {
     # If set to 1, doesn't compile debug symbols into webcore reducing the
     # size of the binary and increasing the speed of gdb.  gcc only.
     'remove_webcore_debug_symbols%': 0,
-    # Set to 1 to enable the clang plugin that checks the usage of the Blink
-    # garbage-collection infrastructure during compilation.
     'enable_oilpan%': 0,
-    'blink_gc_plugin%': 0,
+    # If set to 1 (default) and using clang, the Blink GC plugin will check the
+    # usage of the garbage-collection infrastructure during compilation.
+    'blink_gc_plugin%': 1,
+    # If set to 1 together with blink_gc_plugin, the Blink GC plugin will dump
+    # points-to graph files for each compilation unit.
     'blink_gc_plugin_dump_graph%': 0,
   },
   'targets': [
   {
     'target_name': 'config',
     'type': 'none',
     'direct_dependent_settings': {
       'include_dirs': [
         '.',
         '..',
@@ skipping 77 matching lines @@
       'xcode_settings': {
         'WARNING_CFLAGS!': ['-Wglobal-constructors'],
       },
       'variables': {
         'chromium_code': 1,
       },
     },
   }
   ],
 }