Default enable the Blink GC plugin.

Source/config.gyp

Index: Source/config.gyp
diff --git a/Source/config.gyp b/Source/config.gyp
index dd51af1fbe550e0c7b6aac52a79f942938bc4cde..08fdfd1f732bc6044da4364f9304e08ba4a2b7ea 100644
--- a/Source/config.gyp
+++ b/Source/config.gyp
@@ -32,10 +32,12 @@
     # 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': [