diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index e533507..96cdbf1 100755
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -410,6 +410,10 @@
 def CheckNoStreamUsageIsAdded(input_api, output_api,
                               error_formatter=_ReportErrorFileAndLineNumber):
   """Make sure that no more dependencies on stringstream are added."""
+  with _AddToPath(input_api.os_path.join(
+      input_api.PresubmitLocalPath(), 'tools_webrtc', 'presubmit_checks_lib')):
+    from gn_refs import DefaultGnProject, BelongsToTestTarget
+
   error_msg = ('Usage of <sstream>, <istream> and <ostream> in WebRTC is '
                'deprecated.\n'
                'This includes the following types:\n'
@@ -433,13 +437,15 @@
   usage_re = input_api.re.compile(r'std::(w|i|o|io|wi|wo|wio)(string)*stream')
   no_presubmit_re = input_api.re.compile(
       r'  // no-presubmit-check TODO\(webrtc:8982\)')
-  for f in input_api.AffectedSourceFiles(input_api.FilterSourceFile):
-    if f.LocalPath() == 'PRESUBMIT.py':
-      continue
-    for line_num, line in f.ChangedContents():
-      if ((include_re.search(line) or usage_re.search(line))
-          and not no_presubmit_re.search(line)):
-        errors.append(error_formatter(f.LocalPath(), line_num))
+  is_cpp_file = lambda f: f.LocalPath().endswith(('.cc', '.h'))
+  with DefaultGnProject() as out_dir:
+    for f in input_api.AffectedFiles(file_filter=is_cpp_file):
+      if BelongsToTestTarget(f.LocalPath(), out_dir):
+        continue
+      for line_num, line in f.ChangedContents():
+        if ((include_re.search(line) or usage_re.search(line))
+            and not no_presubmit_re.search(line)):
+          errors.append(error_formatter(f.LocalPath(), line_num))
   if errors:
     return [output_api.PresubmitError(error_msg, errors)]
   return []
diff --git a/tools_webrtc/presubmit_checks_lib/gn_refs.py b/tools_webrtc/presubmit_checks_lib/gn_refs.py
new file mode 100644
index 0000000..3f062eb
--- /dev/null
+++ b/tools_webrtc/presubmit_checks_lib/gn_refs.py
@@ -0,0 +1,70 @@
+# Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
+#
+# Use of this source code is governed by a BSD-style license
+# that can be found in the LICENSE file in the root of the source
+# tree. An additional intellectual property rights grant can be found
+# in the file PATENTS.  All contributing project authors may
+# be found in the AUTHORS file in the root of the source tree.
+
+import os
+import shutil
+import subprocess
+import sys
+import tempfile
+from contextlib import contextmanager
+
+
+# The module find_depot_tools lives into the ./build directory.
+SCRIPT_DIR = os.path.dirname(os.path.abspath(__file__))
+SRC_DIR = os.path.normpath(os.path.join(SCRIPT_DIR, os.pardir, os.pardir))
+sys.path.append(os.path.join(SRC_DIR, 'build'))
+import find_depot_tools
+
+
+@contextmanager
+def DefaultGnProject():
+  """Generates a GN projects with defaul args and returns the path to it."""
+  out_dir = tempfile.mkdtemp('gn')
+  gen_command = [
+    sys.executable,
+    os.path.join(find_depot_tools.DEPOT_TOOLS_PATH, 'gn.py'),
+    'gen',
+    out_dir,
+  ]
+  subprocess.check_output(gen_command)
+  try:
+    yield out_dir
+  finally:
+    shutil.rmtree(out_dir, ignore_errors=True)
+
+
+def BelongsToTestTarget(file_path, out_dir):
+  """Returns True if file_path is part of a testonly build target.
+
+  This function relies on 'gn refs'. It actually runs:
+  $ gn refs <out_dir> file_path --testonly=true`
+
+  Which returns a list of build targets containing file_path (well, only
+  one build target should own a file, but that is not a strict rule).
+
+  If the list is empty, it means the file is owned by a non-testonly build
+  target and the function will return False. Otherwise it will return True.
+
+  Args:
+    file_path: string with the local path of the file to analyze.
+    out_dir: the path to the GN out directory to analyze.
+
+  Returns:
+    boolean: True if the file belongs to a testonly build target.
+  """
+  refs_command = [
+    sys.executable,
+    os.path.join(find_depot_tools.DEPOT_TOOLS_PATH, 'gn.py'),
+    'refs',
+    out_dir,
+    file_path,
+    '--testonly=true'
+  ]
+  output = subprocess.check_output(refs_command)
+  # If file_path belongs to a test target, output will contain a list of them.
+  return output != ''