Add a new bench that tests a simple image filter DAG.

gyp/bench.gypi

 {
   'include_dirs': [
     '../src/core',
     '../src/effects',
     '../src/utils',
     '../tools',
   ],
   'dependencies': [
     'skia_lib.gyp:skia_lib',
   ],
@@ skipping 26 matching lines @@
     '../bench/FontCacheBench.cpp',
     '../bench/FontScalerBench.cpp',
     '../bench/GameBench.cpp',
     '../bench/GrMemoryPoolBench.cpp',
     '../bench/GrResourceCacheBench.cpp',
     '../bench/GrOrderedSetBench.cpp',
     '../bench/GradientBench.cpp',
     '../bench/HairlinePathBench.cpp',
     '../bench/ImageCacheBench.cpp',
     '../bench/ImageDecodeBench.cpp',
+    '../bench/ImageFilterDAGBench.cpp',
     '../bench/InterpBench.cpp',
     '../bench/LightingBench.cpp',
     '../bench/LineBench.cpp',
     '../bench/MagnifierBench.cpp',
     '../bench/MathBench.cpp',
     '../bench/Matrix44Bench.cpp',
     '../bench/MatrixBench.cpp',
     '../bench/MatrixConvolutionBench.cpp',
     '../bench/MemoryBench.cpp',
     '../bench/MemsetBench.cpp',
@@ skipping 24 matching lines @@
     '../bench/StrokeBench.cpp',
     '../bench/TableBench.cpp',
     '../bench/TextBench.cpp',
     '../bench/TileBench.cpp',
     '../bench/VertBench.cpp',
     '../bench/WritePixelsBench.cpp',
     '../bench/WriterBench.cpp',
     '../bench/XfermodeBench.cpp',
   ],
 }