GN: get echo-headers sources via exec_script

BUILD.gn

 # Copyright 2016 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 declare_args() {
 }
 
 skia_public_includes = [
   "include/android",
@@ skipping 267 matching lines @@
       "src/ports/SkImageGeneratorCG.cpp",
     ]
     libs += [ "ApplicationServices.framework" ]
   }
 
   if (is_fuchsia) {
     sources += [ "src/ports/SkFontMgr_empty_factory.cpp" ]
   }
 }
 
+skia_h_headers = exec_script("gyp/find.py",
+                             [ "*.h" ] + rebase_path(skia_public_includes),
+                             "list lines",
+                             []) -
+                 [
+                   rebase_path("include/gpu/gl/GrGLConfig_chrome.h"),
+                   rebase_path("include/gpu/vk/GrVkBackendContext.h"),
+                   rebase_path("include/gpu/vk/GrVkDefines.h"),
+                   rebase_path("include/gpu/vk/GrVkInterface.h"),
+                   rebase_path("include/gpu/vk/GrVkTypes.h"),
+                   rebase_path("include/ports/SkFontMgr_fontconfig.h"),
+                 ]
+
 action("skia.h") {
   script = "gn/echo_headers.py"
   args = [ rebase_path("$target_gen_dir/skia.h", root_build_dir) ] +
-         rebase_path(skia_public_includes, root_build_dir)
-  inputs = [ ".git/logs/HEAD" ]   # ~~> Run any time GIT state changes.
+         rebase_path(skia_h_headers, root_build_dir)
   outputs = [
     "$target_gen_dir/skia.h",
   ]
 }
 
 executable("fiddle") {
   include_dirs = [ "$target_gen_dir" ]
   libs = []
   if (is_linux) {
     libs += [ "OSMesa" ]
@@ skipping 91 matching lines @@
     "tools/sk_tool_utils_font.cpp",
     "tools/timer/Timer.cpp",
   ]
   deps = [
     ":flags",
   ]
 }
 
 gm_sources = exec_script("gyp/find.py",
                          [
+                           "*.c*",
                            rebase_path("gm"),
-                           "*.c*",
                          ],
                          "list lines",
                          [])
 test_lib("gm") {
   public_include_dirs = [ "gm" ]
   sources = gm_sources
   deps = [
     ":gpu_tool_utils",
     ":skia",
     ":tool_utils",
   ]
 }
 
 bench_sources = exec_script("gyp/find.py",
                             [
+                              "*.c*",
                               rebase_path("bench"),
-                              "*.c*",
                             ],
                             "list lines",
                             [])
 
 test_lib("bench") {
   public_include_dirs = [ "bench" ]
   sources = bench_sources
   sources -= [
     rebase_path("bench/nanobench.cpp"),
     rebase_path("bench/nanobenchAndroid.cpp"),
@@ skipping 50 matching lines @@
       ":flags",
       ":gm",
       ":gpu_tool_utils",
       ":skia",
       ":tool_utils",
       "//third_party/jsoncpp",
     ]
     testonly = true
   }
 }