GN WebView: make system_webview_apk work

.gn

 # This file is used by the GN meta build system to find the root of the source
 # tree and to set startup options. For documentation on the values set in this
 # file, run "gn help dotfile" at the command line.
 
 # The location of the build configuration file.
 buildconfig = "//build/config/BUILDCONFIG.gn"
 
 # The secondary source root is a parallel directory tree where
 # GN build files are placed when they can not be placed directly
 # in the source tree, e.g. for third party source trees.
@@ skipping 270 matching lines @@
   "//chrome/chrome_tests.gni",
   "//chrome/common/BUILD.gn",
   "//chrome/common/extensions/api/schemas.gni",
   "//chrome/renderer/BUILD.gn",
   "//chrome/test/BUILD.gn",
   "//chrome/utility/BUILD.gn",
   "//chromeos/BUILD.gn",
 
   # TODO(dgn): Layer violation but breaks the build otherwise, see
   # https://crbug.com/474506
+  "//clank/android_webview/BUILD.gn",
   "//clank/java/BUILD.gn",
   "//clank/native/BUILD.gn",
 
   "//components/domain_reliability/BUILD.gn",
   "//components/scheduler/scheduler.gni",
   "//content/browser/browser.gni",
   "//content/child/child.gni",
   "//content/common/common.gni",
   "//content/content.gni",
   "//content/public/android/BUILD.gn",
@@ skipping 47 matching lines @@
   "//tools/gn/format_test_data/055.golden",
   "//tools/gn/function_exec_script.cc",
   "//tools/gn/gn.gyp",
   "//tools/gn/input_conversion.cc",
   "//tools/gn/misc/emacs/gn.el",
   "//tools/gn/misc/vim/syntax/gn.vim",
   "//tools/gn/setup.cc",
   "//ui/accessibility/BUILD.gn",
   "//ui/views/BUILD.gn",
 ]