Allow usage of stringstream under examples/.

This CL addresses comment #56 on webrtc:8982 [1].

[1] - https://bugs.chromium.org/p/webrtc/issues/detail?id=8982#c56

Bug: webrtc:8982
Change-Id: Iaf56fbcdae4937db1ee6e550d2300d29b6975cfd
No-Try: True
Reviewed-on: https://webrtc-review.googlesource.com/c/110720
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25619}
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 797fb2d..0bcf997 100755
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -481,7 +481,8 @@
   file_filter = lambda x: (input_api.FilterSourceFile(x)
                            and source_file_filter(x))
   for f in input_api.AffectedSourceFiles(file_filter):
-    if f.LocalPath() == 'PRESUBMIT.py':
+    # Usage of stringstream is allowed under examples/.
+    if f.LocalPath() == 'PRESUBMIT.py' or f.LocalPath().startswith('examples'):
       continue
     for line_num, line in f.ChangedContents():
       if ((include_re.search(line) or usage_re.search(line))