verify_dynamic_libraries: py3 compat

Bug: 1158410
Change-Id: Ic8f006dbb391699016a608c9cf328ea269b9e66c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2590054Reviewed-by: Dirk Pranke <dpranke@google.com>
Auto-Submit: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836684}

chrome/tools/build/mac/verify_dynamic_libraries.py

@@ -29,7 +29,7 @@ def verify_image_libraries(image_path, allowed_libraries, binary_path):
     """
     output = subprocess.check_output(
         [binary_path + 'llvm-objdump', '--macho', '--dylibs-used', image_path])
-    output = unicode(output, encoding='utf8').strip()
+    output = output.decode('utf8').strip()
 
     disallowed_libraries = []