gm to illustrate mipmap layer choice

gyp/gmslides.gypi

 # include this gypi to include all the golden master slides.
 {
   'include_dirs': [
     '../gm',
     # include dirs needed by particular GMs
     '../src/utils/debugger',
     '../src/images',
     '../src/lazy',
   ],
   'conditions': [
@@ skipping 115 matching lines @@
         '../gm/imagefilterscropexpand.cpp',
         '../gm/imagefiltersgraph.cpp',
         '../gm/imagefiltersscaled.cpp',
         '../gm/internal_links.cpp',
         '../gm/lcdtext.cpp',
         '../gm/linepaths.cpp',
         '../gm/matrixconvolution.cpp',
         '../gm/matriximagefilter.cpp',
         '../gm/megalooper.cpp',
         '../gm/mixedxfermodes.cpp',
+        '../gm/mipmap.cpp',
         '../gm/modecolorfilters.cpp',
         '../gm/morphology.cpp',
         '../gm/multipicturedraw.cpp',
         '../gm/nested.cpp',
         '../gm/ninepatchstretch.cpp',
         '../gm/nonclosedpaths.cpp',
         '../gm/offsetimagefilter.cpp',
         '../gm/ovals.cpp',
         '../gm/patch.cpp',
         '../gm/patchgrid.cpp',
@@ skipping 106 matching lines @@
         '../gm/shadertext2.cpp',
         '../gm/shadertext3.cpp',
 
         # TODO(reed): Allocates more memory than Android devices are capable of
         # fulfilling. See http://skbug.com/1978
         '../gm/verylargebitmap.cpp',
       ],
     }],
   ],
 }