GN: get echo-headers sources via exec_script

gyp/gmslides.gypi

 # Copyright 2015 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 # include this gypi to include all the golden master slides.
 {
   'include_dirs': [
     '../gm',
     # include dirs needed by particular GMs
     '../include/client/android',
     '../tools/debugger',
     '../src/effects/gradients',
     '../src/images',
     '../src/lazy',
   ],
   'conditions': [
     # If we're building SampleApp on the bots, no need to link in the GM slides.
     # We're not going to run it; we're only making sure it still builds.
     # It'd be nice to do this in SampleApp.gypi, but I can't find a way to make it work.
     [ 'not ("<(_target_name)" == "SampleApp" and skia_is_bot)', {
       'sources': [
-        '<!@(python find.py ../gm "*.c*")',
+        '<!@(python find.py "*.c*" ../gm)',
 
         # Files needed by particular GMs
         '../src/gpu/batches/GrTestBatch.h',
         '../tools/debugger/SkDrawCommand.h',
         '../tools/debugger/SkDrawCommand.cpp',
         '../tools/debugger/SkDebugCanvas.h',
         '../tools/debugger/SkDebugCanvas.cpp',
         '../tools/debugger/SkJsonWriteBuffer.h',
         '../tools/debugger/SkJsonWriteBuffer.cpp',
         '../tools/debugger/SkObjectParser.h',
         '../tools/debugger/SkObjectParser.cpp',
         '../tools/debugger/SkOverdrawMode.h',
         '../tools/debugger/SkOverdrawMode.cpp',
       ],
       'dependencies': [
         'libpng.gyp:libpng',
         'tools.gyp:picture_utils',
       ]
     }],
   ],
 }