reenable the scale benchmark, and only bench actual canvas draw commands

gyp/bench.gypi

 # sources and conditions used in skia's bench.gyp and chromium's skia.gyp
 #
 {
   'sources': [
     '../bench/benchmain.cpp',
     '../bench/SkBenchmark.h',
     '../bench/SkBenchmark.cpp',
     '../bench/AAClipBench.cpp',
     '../bench/BicubicBench.cpp',
     '../bench/BitmapBench.cpp',
     '../bench/BitmapRectBench.cpp',
+    '../bench/BitmapScaleBench.cpp',
     '../bench/BlendBench.cpp',
     '../bench/BlurBench.cpp',
     '../bench/BlurImageFilterBench.cpp',
     '../bench/BlurRectBench.cpp',
     '../bench/ChecksumBench.cpp',
     '../bench/ChartBench.cpp',
     '../bench/ChromeBench.cpp',
     '../bench/CmapBench.cpp',
     '../bench/ColorFilterBench.cpp',
     '../bench/DashBench.cpp',
@@ skipping 51 matching lines @@
     '../bench/TimerData.h',
     '../bench/TimerData.cpp',
   ],
 }
 
 # Local Variables:
 # tab-width:2
 # indent-tabs-mode:nil
 # End:
 # vim: set expandtab tabstop=2 shiftwidth=2: