Remove impeller-cmake build rules (#171407)

We no longer have any stakeholders relying on the impeller-cmake build,
and I am no longer maintaining it.

Developers who wish to use the Impeller renderer in native applications
should consider using the awesome [Impeller Standalone C
SDK](https://github.com/flutter/flutter/tree/master/engine/src/flutter/impeller/toolkit/interop#impeller-standalone-sdk)
built by @chinmaygarde instead.

Author: bdero

DEPS

@@ -130,12 +130,6 @@ vars = {
   # RBE will be downloaded from CIPD. This option is only usable by Googlers.
   'use_rbe': False,
 
-  # This is not downloaded be default because it increases the
-  # `gclient sync` time by between 1 and 3 minutes. This option is enabled
-  # in flutter/ci/builders/mac_impeller_cmake_example.json, and is likely to
-  # only be useful locally when reproducing issues found by the bot.
-  'download_impeller_cmake_example': False,
-
   # Upstream URLs for third party dependencies, used in
   # determining common ancestor commit for vulnerability scanning
   # prefixed with 'upstream_' in order to be identified by parsing tool.
@@ -845,23 +839,6 @@ deps = {
      'dep_type': 'cipd',
    },
 
-  'engine/src/flutter/third_party/impeller-cmake-example': {
-     'url': Var('flutter_git') + '/third_party/impeller-cmake-example.git' + '@' + '9f8298ec31dcbebbf019bd487888166abf2f55e6',
-     'condition': 'download_impeller_cmake_example',
-  },
-
-  # cmake is only used by impeller-cmake-example.
-  'engine/src/flutter/buildtools/mac-x64/cmake': {
-    'packages': [
-      {
-        'package': 'infra/3pp/tools/cmake/mac-amd64',
-        'version': 'CGpMvZoP962wdEINR9d4OEvEW7ZOv0MPrHNKbBUBS0sC',
-      }
-    ],
-    'condition': 'download_impeller_cmake_example and host_os == "mac"',
-    'dep_type': 'cipd',
-  },
-
   'engine/src/flutter/third_party/google_fonts_for_unit_tests': {
       'packages': [
         {
@@ -965,18 +942,6 @@ hooks = [
       'engine/src/flutter/tools/githooks/setup.py',
     ]
   },
-  {
-    'name': 'impeller-cmake-example submodules',
-    'pattern': '.',
-    'condition': 'download_impeller_cmake_example',
-    'action': [
-      'python3',
-      'engine/src/flutter/ci/impeller_cmake_build_test.py',
-      '--path',
-      'flutter/third_party/impeller-cmake-example',
-      '--setup',
-    ]
-  },
   {
     'name': 'Download Fuchsia system images',
     'pattern': '.',

engine/src/flutter/ci/impeller_cmake_build_test.py

@@ -865,28 +865,6 @@ def to_gn_wasm_args(args, gn_args):
   gn_args['flutter_prebuilt_dart_sdk'] = True
 
 
-def run_impeller_cmake(args):
-  impeller_cmake_dir = os.path.join('flutter', 'third_party', 'impeller-cmake-example')
-  if not os.path.isdir(os.path.join(SRC_ROOT, impeller_cmake_dir)):
-    print('The Impeller cmake example directory "{}" does not exist'.format(impeller_cmake_dir))
-    return 1
-  cmake_cmd = [
-      'python3',
-      os.path.join(SRC_ROOT, 'flutter', 'ci', 'impeller_cmake_build_test.py'),
-      '--path',
-      impeller_cmake_dir,
-      '--cmake',
-  ]
-  if args.xcode_symlinks:
-    cmake_cmd = cmake_cmd + ['--xcode-symlinks']
-  try:
-    cmake_call_result = subprocess.call(cmake_cmd, cwd=SRC_ROOT)
-  except subprocess.CalledProcessError as exc:
-    print('Failed to generate cmake files: ', exc.returncode, exc.output)
-    return 1
-  return cmake_call_result
-
-
 def parse_args(args):
   args = args[1:]
   parser = argparse.ArgumentParser(description='A script to run `gn gen`.')
@@ -1198,13 +1176,6 @@ def parse_args(args):
 
   parser.add_argument('--malioc-path', type=str, help='The path to the malioc tool.')
 
-  parser.add_argument(
-      '--impeller-cmake-example',
-      default=False,
-      action='store_true',
-      help='Do not run GN. Instead configure the Impeller cmake example build.',
-  )
-
   parser.add_argument(
       '--slimpeller',
       default=False,
@@ -1274,9 +1245,6 @@ def main(argv):
   args = parse_args(argv)
   validate_args(args)
 
-  if args.impeller_cmake_example:
-    return run_impeller_cmake(args)
-
   exe = '.exe' if sys.platform.startswith(('cygwin', 'win')) else ''
 
   command = [