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

Filter out build/secondary/third_party dependencies to work around
__main__.LicenseError: missing README.chromium or licenses.py SPECIAL_CASES entry in build/secondary/third_party/android_tools

BUG=606859
BUG=710801
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_cronet_tester

Review-Url: https://codereview.chromium.org/2959303002
Cr-Commit-Position: refs/heads/master@{#485291}

components/cronet/android/BUILD.gn

@@ -1201,13 +1201,17 @@ jar_src("jar_cronet_impl_native_java_source") {
 action("generate_licenses") {
   _license_path = "$_package_dir/LICENSE"
 
-  script = "//components/cronet/tools/cronet_licenses.py"
+  script = "//tools/licenses.py"
   outputs = [
     _license_path,
   ]
   args = [
-    "license",
+    "license_file",
     rebase_path(_license_path, root_build_dir),
+    "--gn-target",
+    "//components/cronet/android:cronet",
+    "--gn-out-dir",
+    ".",
   ]
 }
 

tools/licenses.py

@@ -493,7 +493,7 @@ def GetThirdPartyDepsFromGNDepsOutput(gn_deps):
     third_party_deps = set()
     for build_dep in gn_deps.split():
         m = re.search(r'^(.+/third_party/[^/]+)/(.+/)?BUILD\.gn$', build_dep)
-        if m:
+        if m and not os.path.join('build', 'secondary') in build_dep:
             third_party_deps.add(m.group(1))
     return third_party_deps