Add support for system snappy.

build/linux/unbundle/snappy.gyp

Index: build/linux/unbundle/snappy.gyp
diff --git a/build/linux/unbundle/libevent.gyp b/build/linux/unbundle/snappy.gyp
similarity index 66%
copy from build/linux/unbundle/libevent.gyp
copy to build/linux/unbundle/snappy.gyp
index 99d743533f6104c78d5106fa445f642f5eda2514..ab856ed89cb9d21c8b71bb9f1f04a80bb8323d66 100644
--- a/build/linux/unbundle/libevent.gyp
+++ b/build/linux/unbundle/snappy.gyp
@@ -5,13 +5,15 @@
 {
   'targets': [
     {
-      'target_name': 'libevent',
+      'target_name': 'snappy',
       'type': 'none',
-      'toolsets': ['host', 'target'],
       'variables': {
-        'headers_root_path': '.',
+        'headers_root_path': 'src',
         'header_filenames': [
-          'event.h',
+          'snappy-c.h',
+          'snappy-sinksource.h',
+          'snappy-stubs-public.h',
+          'snappy.h',
         ],
       },
       'includes': [
@@ -19,9 +21,9 @@
       ],
       'link_settings': {
         'libraries': [
-          '-levent',
+          '-lsnappy',
         ],
       },
-    }
+    },
   ],
 }