Add JSON output option to bench.

gyp/bench.gyp

 # GYP file to build performance testbench.
 #
 {
   'includes': [
     'apptype_console.gypi',
   ],
   'targets': [
     {
       'target_name': 'bench',
       'type': 'executable',
       'include_dirs' : [
         '../src/core',
         '../src/effects',
         '../src/utils',
       ],
       'dependencies': [
         'skia_lib.gyp:skia_lib',
         'bench_timer',
         'flags.gyp:flags',
+        'jsoncpp.gyp:jsoncpp',
       ],
       'sources': [
         '../bench/AAClipBench.cpp',
         '../bench/BicubicBench.cpp',
         '../bench/BitmapBench.cpp',
         '../bench/BitmapRectBench.cpp',
         '../bench/BitmapScaleBench.cpp',
         '../bench/BlurBench.cpp',
         '../bench/BlurImageFilterBench.cpp',
         '../bench/BlurRectBench.cpp',
@@ skipping 126 matching lines @@
         ['skia_gpu == 1', {
           'sources': [
             '../bench/BenchGpuTimer_gl.h',
             '../bench/BenchGpuTimer_gl.cpp',
           ],
         }],
       ],
     }
   ],
 }