GN: enable Vulkan on Android when API >= 24.

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.
 
 import("gn/shared_sources.gni")
 
 declare_args() {
   skia_enable_tools = !is_fuchsia && !is_component_build
 
   skia_use_expat = true
   skia_use_fontconfig = is_linux
   skia_use_freetype = is_android || is_fuchsia || is_linux
   skia_use_giflib = !is_fuchsia
   skia_use_libjpeg_turbo = true
   skia_use_libpng = true
   skia_use_libwebp = !is_fuchsia
   skia_use_sfntly = !is_fuchsia
-  skia_use_vulkan = false
+  skia_use_vulkan = is_android && defined(ndk_api) && ndk_api >= 24
   skia_use_zlib = true
 }
 
 fontmgr_android_enabled = skia_use_expat && skia_use_freetype
 
 skia_public_includes = [
   "include/android",
   "include/c",
   "include/codec",
   "include/config",
@@ skipping 809 matching lines @@
     sources = [
       "tools/SkShaper_primitive.cpp",
       "tools/using_skia_and_harfbuzz.cpp",
     ]
     deps = [
       ":skia",
     ]
     testonly = true
   }
 }