Add dependency on chromium/src/build for Mac/iOS build (#4224)

* Add dependency on chromium/src/build for Mac/iOS build

Preparation for migrating to mac_toolchain.py for installing/configuring
Xcode versions on the Mac build bots.

* Exclude third_party/chromium_build from licence script

It's used only at build time to fetch and install the correct Xcode
version.

DEPS

@@ -98,7 +98,11 @@ vars = {
   'dart_web_socket_channel_tag': '1.0.6',
   'dart_yaml_tag': '2.1.12',
 
+  # Chromium build tooling used for Mac/iOS builds
+  'chromium_build_revision': 'b6fbb0db634b8e8380b718eba27f077d94a6d09c',
+
   # Build bot tooling for iOS
+  # TODO(cbracken) delete once migrated to chromium tooling above
   'ios_tools_revision': '69b7c1b160e7107a6a98d948363772dc9caea46f',
 
   'buildtools_revision': '5b8eb38aaf523f0124756454276cd0a5b720c17e',
@@ -151,6 +155,9 @@ deps = {
   'src/ios_tools':
    Var('chromium_git') + '/chromium/src/ios.git' + '@' + Var('ios_tools_revision'),
 
+  'third_party/chromium_build':
+   Var('chromium_git') + '/chromium/src/build.git' + '@' + Var('chromium_build_revision'),
+
   'src/third_party/icu':
    Var('chromium_git') + '/chromium/deps/icu.git' + '@' + '08cb956852a5ccdba7f9c941728bb833529ba3c6',
 

tools/licenses/lib/main.dart

@@ -1200,6 +1200,12 @@ class RepositoryGenericThirdPartyDirectory extends RepositoryDirectory {
 
   @override
   bool get subdirectoriesAreLicenseRoots => true;
+
+  @override
+  bool shouldRecurse(fs.IoNode entry) {
+    return entry.name != 'chromium_build' // only used by build
+        && super.shouldRecurse(entry);
+  }
 }
 
 class RepositoryReachOutFile extends RepositoryLicensedFile {