GN: get echo-headers sources via exec_script

gyp/viewer.gyp

 # Copyright 2016 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 # GYP file to build performance testbench.
 #
 {
   'includes': [
     'apptype_console.gypi',
   ],
@@ skipping 13 matching lines @@
         '../src/effects',
         '../src/gpu',
         '../src/image',
         '../src/images',
         '../src/pathops',
         '../src/views/unix',
         '../tools/timer',
       ],
       'sources': [
         '../gm/gm.cpp',
-        '<!@(python find.py ../tools/viewer "*.cpp")',
+        '<!@(python find.py "*.cpp" ../tools/viewer)',
 
         # views (subset of files for the Android build)
         '../src/views/SkEvent.cpp',
         '../src/views/SkEventSink.cpp',
         '../src/views/SkOSMenu.cpp',
         '../src/views/SkTagList.cpp',
         '../src/views/SkTagList.h',
         '../src/views/SkTouchGesture.cpp',
         '../src/views/SkView.cpp',
         '../src/views/SkViewPriv.cpp',
         '../src/views/SkViewPriv.h',
         '../src/views/unix/keysym2ucs.c',
       ],
       'sources!': [
         '../samplecode/SampleSkLayer.cpp', #relies on SkMatrix44 which doesn't compile
         '../samplecode/SampleFontCache.cpp', #relies on pthread.h
-      ],      
+      ],
       'dependencies': [
         'flags.gyp:flags',
         'gputest.gyp:skgputest',
         'jsoncpp.gyp:jsoncpp',
         'skia_lib.gyp:skia_lib',
         'tools.gyp:crash_handler',
         'tools.gyp:proc_stats',
         'tools.gyp:resources',
         'tools.gyp:sk_tool_utils',
         'tools.gyp:timer',
@@ skipping 44 matching lines @@
           ],
         }],
         ['skia_vulkan == 0', {
           'sources/': [ ['exclude', 'Vulkan']
           ],
         }],
       ],
     },
   ],
 }