[Lorenz] Change working directory before running gn

This should fix the failure in the builder and allow the script to be
run from any directory.

Bug: 1111056
Change-Id: Ibecfbe763a18bf4fcc5f227d23ce42edee3a2ebf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2369011Reviewed-by: Mohamed Heikal <mheikal@chromium.org>
Commit-Queue: Henrique Nakashima <hnakashima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801009}

tools/android/dependency_analysis/generate_json_dependency_graph.py

@@ -9,6 +9,7 @@ import functools
 import math
 import multiprocessing
 import pathlib
+import os
 import subprocess
 import sys
 
@@ -189,6 +190,9 @@ def main():
                             help='Path to the gn executable.')
     arguments = arg_parser.parse_args()
 
+    # gn must be run from inside the git checkout.
+    os.chdir(SRC_PATH)
+
     print('Getting list of dependency jars...')
     gn_desc_output = _run_gn_desc_list_dependencies(arguments.build_output_dir,
                                                     arguments.target,