[Cronet] Use gn desc to find third party licenses on Android.

tools/licenses.py

 #!/usr/bin/env python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Utility for checking and processing licensing information in third_party
 directories.
 
 Usage: licenses.py <command>
 
@@ skipping 475 matching lines @@
     """Returns third_party/foo directories given the output of "gn desc deps".
 
     Note that it always returns the direct sub-directory of third_party
     where README.chromium and LICENSE files are, so that it can be passed to
     ParseDir(). e.g.:
         .../third_party/cld_3/src/src/BUILD.gn -> .../third_party/cld_3
     """
     third_party_deps = set()
     for build_dep in gn_deps.split():
         m = re.search(r'^(.+/third_party/[^/]+)/(.+/)?BUILD\.gn$', build_dep)
-        if m:
+        # TODO(phajdan): Consider using PRUNE_PATHS to filter unwanted deps.

[Paweł Hajdan Jr., 2017/06/30 07:16:05]

Why does this TODO add me? It should add the person who has more context... you?
;-)

[mef, 2017/06/30 12:38:40]

I'll be happy to leave it as is or use PRUNE_PATHS if that makes sense, which I
don't know. 
Do you know, who is a proper person to ask?

The technical difficulty I ran into here is that PRUNE_PATHS contain relative
paths, but |build_dep| contains the absolute one, so naive 'build_dep in
PRUNE_PATHS' doesn't work.

[mef, 2017/06/30 14:31:45]

I've played with relpath and PRUNE_PATHS and it looks ugly.
The problematic directory is 'build/secondary/third_party/android_tools' so
naive check for it being in PRUNE_PATHS doesn't work.

I think that current check is reasonably good and can stay. WDYT?
 

+        if m and not os.path.join("secondary", "third_party") in build_dep:
             third_party_deps.add(m.group(1))
     return third_party_deps
 
 
 def FindThirdPartyDeps(gn_out_dir, gn_target):
     if not gn_out_dir:
         raise RuntimeError("--gn-out-dir is required if --gn-target is used.")
 
     # Generate gn project in temp directory and use it to find dependencies.
     # Current gn directory cannot be used when we run this script in a gn action
@@ skipping 225 matching lines @@
         if not GenerateLicenseFile(
                 args.output_file, args.gn_out_dir, args.gn_target):
             return 1
     else:
         print __doc__
         return 1
 
 
 if __name__ == '__main__':
   sys.exit(main())