GN: get echo-headers sources via exec_script

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index d941fe400de18297974eca52a4fdf1e44fed0b78..5ac22ad2cd6793be801e6b49b46cbe0179fa6b3a 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -285,11 +285,23 @@ component("skia") {
   }
 }
 
+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",
   ]
@@ -401,8 +413,8 @@ test_lib("tool_utils") {
 
 gm_sources = exec_script("gyp/find.py",
                          [
-                           rebase_path("gm"),
                            "*.c*",
+                           rebase_path("gm"),
                          ],
                          "list lines",
                          [])
@@ -418,8 +430,8 @@ test_lib("gm") {
 
 bench_sources = exec_script("gyp/find.py",
                             [
-                              rebase_path("bench"),
                               "*.c*",
+                              rebase_path("bench"),
                             ],
                             "list lines",
                             [])