gm: add a flag to force perspective usage in all gms

gyp/SampleApp.gyp

 {
   'variables': {
     #manually set sample_pdf_file_viewer to 1 to have the PdfViewer in SampleApp
     'sample_pdf_file_viewer%': 0,
   },
   'targets': [
     {
       'target_name': 'SampleApp',
       'type': 'executable',
       'mac_bundle' : 1,
@@ skipping 132 matching lines @@
         '../src/utils/SkLua.cpp',
       ],
       'sources!': [
         '../samplecode/SampleSkLayer.cpp', #relies on SkMatrix44 which doesn't compile
         '../samplecode/SampleTests.cpp',   #includes unknown file SkShaderExtras.h
         '../samplecode/SampleWarp.cpp',
         '../samplecode/SampleFontCache.cpp',
       ],
       'dependencies': [
         'skia_lib.gyp:skia_lib',
+        'flags.gyp:flags',
         'views.gyp:views',
         'animator.gyp:animator',
         'xml.gyp:xml',
         'experimental.gyp:experimental',
         'pdf.gyp:pdf',
         'views_animated.gyp:views_animated',
         'lua.gyp:lua',
       ],
      'conditions' : [
        [ 'sample_pdf_file_viewer == 1', {
@@ skipping 157 matching lines @@
       },
     },
   ],
 }
 
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