Allow GMs to be used as benchmarks. Make convex_poly_clip opt in.

R=reed@google.com

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/151843002

git-svn-id: http://skia.googlecode.com/svn/trunk@13279 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gyp/bench.gyp b/gyp/bench.gyp
index d404000..c408d7c 100644
--- a/gyp/bench.gyp
+++ b/gyp/bench.gyp
@@ -97,6 +97,9 @@
         '../bench/SkBenchLogger.h',
         '../bench/SkBenchmark.cpp',
         '../bench/SkBenchmark.h',
+        '../bench/SkGMBench.cpp',
+        '../bench/SkGMBench.h',
+
         '../bench/benchmain.cpp',
       ],
       'conditions': [
@@ -111,6 +114,9 @@
           },
         ],
       ],
+      'includes': [
+        'gmslides.gypi',
+      ],
     },
     {
       'target_name' : 'bench_timer',