Add presubmit check to prevent package boundary violations.

PRESUBMIT.py

Index: PRESUBMIT.py
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 276db1e83b92d74b715347b5122c207c589bc3aa..a89bf00476e44f5a0efe009ce66a35a05bffe217 100755
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -9,6 +9,7 @@
 import json
 import os
 import re
+import subprocess
 import sys
 
 
@@ -84,6 +85,18 @@ LEGACY_API_DIRS = (
 API_DIRS = NATIVE_API_DIRS[:] + LEGACY_API_DIRS[:]
 
 
+def _RunCommand(command, cwd):
+  """Runs a command and returns the output from that command."""
+  p = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
+                       cwd=cwd)
+  stdout = p.stdout.read()
+  stderr = p.stderr.read()
+  p.wait()
+  p.stdout.close()
+  p.stderr.close()
+  return p.returncode, stdout, stderr
+
+
 def _VerifyNativeApiHeadersListIsValid(input_api, output_api):
   """Ensures the list of native API header directories is up to date."""
   non_existing_paths = []
@@ -285,6 +298,19 @@ def _CheckNoMixingCAndCCSources(input_api, gn_files, output_api):
         items=violating_gn_files.keys())]
   return []
 
+def _CheckNoPackageBoundaryViolations(input_api, gn_files, output_api):

[kjellander_webrtc, 2017/01/19 10:51:26]

nit: +1 blank line for top-level functions.

[ehmaldonado_webrtc, 2017/01/19 13:33:56]

What do you mean? Should I also add a blank line before the functions above?

[kjellander_webrtc, 2017/01/24 09:33:19]

Yeah, all top-level definitions are to be separated with two blank lines
according to the Python style guide (I agree that's a bit silly):
https://google.github.io/styleguide/pyguide.html?showone=Blank_Lines#Blank_Lines

+  cwd = input_api.PresubmitLocalPath()
+  script_path = os.path.join('tools-webrtc', 'check_package_boundaries.py')
+  webrtc_path = os.path.join('webrtc')
+  command = ['python', script_path, '--max_messages=1', webrtc_path]

[kjellander_webrtc, 2017/01/19 10:51:26]

Use sys.executable instead instead of 'python'.  It's what's commonly used and I
think it's safer (avoids problems with incorrect PATH on Windows etc).

[ehmaldonado_webrtc, 2017/01/19 13:33:56]

Done.
I also decided to get rid of --max-messages=1.

[kjellander_webrtc, 2017/01/24 09:33:19]

Acknowledged.

+  command += [gn_file.LocalPath() for gn_file in gn_files]
+  returncode, _, stderr = _RunCommand(command, cwd)
+  if returncode:
+    return [output_api.PresubmitError(
+        'There are package boundary violations in the following GN files:\n\n'
+        '%s' % stderr)]
+  return []
+
 def _CheckGnChanges(input_api, output_api):
   source_file_filter = lambda x: input_api.FilterSourceFile(
       x, white_list=(r'.+\.(gn|gni)$',))
@@ -298,6 +324,8 @@ def _CheckGnChanges(input_api, output_api):
   if gn_files:
     result.extend(_CheckNoSourcesAbove(input_api, gn_files, output_api))
     result.extend(_CheckNoMixingCAndCCSources(input_api, gn_files, output_api))
+    result.extend(_CheckNoPackageBoundaryViolations(
+        input_api, gn_files, output_api))
   return result
 
 def _CheckUnwantedDependencies(input_api, output_api):