Add checkdeps presubmit check. Warns on new #includes of dependencies

tools/checkdeps/checkdeps.py

Index: tools/checkdeps/checkdeps.py
diff --git a/tools/checkdeps/checkdeps.py b/tools/checkdeps/checkdeps.py
index 870e26230a7e68c487768333024385d15d9e5c01..303699c38d6564ea5c615d3cc0a24e480f8f3d26 100755
--- a/tools/checkdeps/checkdeps.py
+++ b/tools/checkdeps/checkdeps.py
@@ -231,6 +231,11 @@ def CheckDirectory(parent_rules, checkers, dir_name):
   return success
 
 
+def ShouldCheckAddedIncludesInFile(file_path):
+  """Whether to check added includes in the given file."""
+  return os.path.splitext(file_path)[1] in cpp_checker.CppChecker.EXTENSIONS
+
+
 def CheckAddedIncludes(added_includes):
   """This is used from PRESUBMIT.py to check new #include statements added in
   the change being presubmit checked.
@@ -288,7 +293,7 @@ def CheckAddedIncludes(added_includes):
   problems = []
   for file_path, include_lines in added_includes:
     # TODO(joi): Make this cover Java as well.
-    if not os.path.splitext(file_path)[1] in cpp.EXTENSIONS:
+    if not ShouldCheckAddedIncludesInFile(file_path):
       pass
     rules_for_file = GetDirectoryRules(os.path.dirname(file_path))
     if rules_for_file: