Use absolute pcs and load locations to symbolize on macOS.

tracing/bin/symbolize_trace_macho_reader.py

+# Copyright 2017 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import re
+import subprocess
+
+
+def ReadMachOTextLoadAddress(file_name):
+  """
+  This function returns the load address of the TEXT segment of a Mach-O file.
+  """
+  regex = re.compile(r".* vmaddr 0x([\dabcdef]*)")
+  cmd = ["otool", "-l", file_name]
+  output = subprocess.check_output(cmd).split('\n')
+  for i in range(len(output) - 3):
+    # It's possible to use a regex here instead, but these conditionals are much
+    # clearer.
+    if ("cmd LC_SEGMENT_64" in output[i] and
+        "cmdsize" in output[i + 1] and
+        "segname __TEXT" in output[i + 2] and
+        "vmaddr" in output[i + 3]):
+      result = regex.match(output[i + 3])
+      assert result
+      return int(result.group(1), 16)
+  return None