Fix mb.py when using `isolate archive`

* luci-go's `isolate archive` requires `-isolate` flag.
* we also enable `-dump-json`, which dumps a JSON file that contains the SHA1 hash of the isolated file.

Tested on the following command:

```
tools/mb/mb.py run -s --no-default-dimensions -d pool chromium.tests -d device_os KTU84P -d device_type hammerhead out/Release/ base_unittests -- --test-filter FakeClass#fakeTest
```

It runs successfully.

Bug: 1062881
Change-Id: I46af6679e43d3af6bfed797485cb485b39235733
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2105272Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Ye Kuang <yekuang@google.com>
Cr-Commit-Position: refs/heads/master@{#751624}

tools/mb/mb.py

@@ -662,16 +662,22 @@ class MetaBuildWrapper(object):
     for k, v in self._DefaultDimensions() + self.args.dimensions:
       dimensions += ['-d', k, v]
 
+    archive_json_path = self.ToSrcRelPath(
+        '%s/%s.archive.json' % (build_dir, target))
     cmd = [
         self.PathJoin(self.chromium_src_dir, 'tools', 'luci-go',
                       self.isolate_exe),
         'archive',
+        '-i',
+        self.ToSrcRelPath('%s/%s.isolate' % (build_dir, target)),
         '-s',
         self.ToSrcRelPath('%s/%s.isolated' % (build_dir, target)),
         '-I',
         isolate_server,
         '-namespace',
         namespace,
+        '-dump-json',
+        archive_json_path,
     ]
 
     # Talking to the isolateserver may fail because we're not logged in.
@@ -693,7 +699,21 @@ class MetaBuildWrapper(object):
 
       return ret
 
-    isolated_hash = out.splitlines()[0].split()[0]
+    try:
+      archive_hashes = json.loads(self.ReadFile(archive_json_path))
+    except Exception:
+      self.Print(
+          'Failed to read JSON file "%s"' % archive_json_path, file=sys.stderr)
+      return 1
+    try:
+      isolated_hash = archive_hashes[target]
+    except Exception:
+      self.Print(
+          'Cannot find hash for "%s" in "%s", file content: %s' %
+          (target, archive_json_path, archive_hashes),
+          file=sys.stderr)
+      return 1
+
     cmd = [
         self.executable,
         self.PathJoin('tools', 'swarming_client', 'swarming.py'),

tools/mb/mb_unittest.py

@@ -831,30 +831,31 @@ class UnitTest(unittest.TestCase):
 
   def test_run_swarmed(self):
     files = {
-      '/fake_src/testing/buildbot/gn_isolate_map.pyl': (
-          "{'base_unittests': {"
-          "  'label': '//base:base_unittests',"
-          "  'type': 'raw',"
-          "  'args': [],"
-          "}}\n"
-      ),
-      '/fake_src/out/Default/base_unittests.runtime_deps': (
-          "base_unittests\n"
-      ),
-      '/fake_src/third_party/depot_tools/cipd_manifest.txt': (
-          "# vpython\n"
-          "/some/vpython/pkg  git_revision:deadbeef\n"
-      ),
+        '/fake_src/testing/buildbot/gn_isolate_map.pyl':
+        ("{'base_unittests': {"
+         "  'label': '//base:base_unittests',"
+         "  'type': 'raw',"
+         "  'args': [],"
+         "}}\n"),
+        '/fake_src/out/Default/base_unittests.runtime_deps':
+        ("base_unittests\n"),
+        '/fake_src/out/Default/base_unittests.archive.json':
+        ("{\"base_unittests\":\"fake_hash\"}"),
+        '/fake_src/third_party/depot_tools/cipd_manifest.txt':
+        ("# vpython\n"
+         "/some/vpython/pkg  git_revision:deadbeef\n"),
     }
 
-    def run_stub(cmd, **_kwargs):
-      if os.path.join('tools', 'luci-go', 'isolate') in cmd[0]:
-        return 0, 'fake_hash base_unittests', ''
-      else:
-        return 0, '', ''
-
     mbw = self.fake_mbw(files=files)
-    mbw.Run = run_stub
+    original_impl = mbw.ToSrcRelPath
+
+    def to_src_rel_path_stub(path):
+      if path.endswith('base_unittests.archive.json'):
+        return 'base_unittests.archive.json'
+      return original_impl(path)
+
+    mbw.ToSrcRelPath = to_src_rel_path_stub
+
     self.check(['run', '-s', '-c', 'debug_goma', '//out/Default',
                 'base_unittests'], mbw=mbw, ret=0)
     self.check(['run', '-s', '-c', 'debug_goma', '-d', 'os', 'Win7',