Output LiteRT-LM benchmark results to file

Write the benchmark metrics output to a proto file instead of stdout,
and include that file in the CAS outputs so that it can be pushed to a
GCS bucket with a results merge script in a follow-up.

For now the file can be manually inspected in the CAS Outputs on the
Swarming Task Page.

Bug: 549160087
Change-Id: I3cb865beb50c08e6de0e1be4f20590e971376089
Cq-Include-Trybots: luci.dawn.try:dawn-try-linux-x64-nvidia-gtx1660-rel
Include-Ci-Only-Tests: ci:dawn-linux-x64-nvidia-gtx1660-rel|litert_lm_benchmark
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/333955
Commit-Queue: Natalie Chouinard <chouinard@google.com>
Reviewed-by: dan sinclair <dsinclair@chromium.org>

scripts/run_litert_lm_benchmark.py

diff --git a/scripts/run_litert_lm_benchmark.py b/scripts/run_litert_lm_benchmark.py
index fead45d..8aeadba 100755
--- a/scripts/run_litert_lm_benchmark.py
+++ b/scripts/run_litert_lm_benchmark.py
@@ -38,7 +38,7 @@
 import subprocess
 
 
-def run_litert_lm() -> subprocess.CompletedProcess:
+def run_litert_lm(metric_proto_file_path: Path) -> subprocess.CompletedProcess:
     repo_root = Path(__file__).resolve().parent.parent
     binary_path = Path.cwd() / 'litert_lm_advanced_main'
     model_path = repo_root / 'third_party' / 'litert-lm' / 'data' / 'model.litertlm'
@@ -48,11 +48,11 @@
         '--benchmark',
         '--backend=gpu',
         f'--model_path={model_path}',
+        f'--metric_proto_file_path={metric_proto_file_path}',
     ]
 
     print(f"Executing: {' '.join(cmd)}")
 
-
     # The .so files are isolated alongside the binary in the current build out directory,
     # so explicitly add them to the library path for execution on Linux bots.
     env = os.environ.copy()
@@ -89,7 +89,15 @@
                         help='Currently unused, needed for bot support.')
     args = parser.parse_args()
 
-    proc = run_litert_lm()
+    # Determine output directory for results.
+    if args.isolated_script_test_output:
+        output_dir = Path(args.isolated_script_test_output).parent
+    else:
+        output_dir = Path.cwd()
+
+    # Run the benchmark and generate metric results file.
+    metric_file = output_dir / 'litert_lm_metrics.pb'
+    proc = run_litert_lm(metric_file)
     if args.isolated_script_test_output:
         generate_results_for_resultdb_ingestion(
             not proc.returncode, args.isolated_script_test_output)