Support specifying the name of the default pool to use

README.md

@@ -144,7 +144,18 @@ def post_configure():
     pass
 ```
 
-### Define large pool
+### Define pools to run on
+
+#### Define default pool
+
+By default, actions will not specify which pool to run on, so they will be run on the default worker
+pool. You can customize the name of the pool to run actions on as follows:
+
+```
+python3 configure_reclient.py --default_pool_name=<NAME_OF_DEFAULT_POOL>
+```
+
+#### Define large pool
 
 Chromium now supports running actions on a different worker pool that might otherwise run into
 an OOM. See [Reclient](https://source.chromium.org/chromium/chromium/src/+/4f94ce92c8c657cbfeb4dd386581340704c9dd11).
@@ -157,4 +168,10 @@ You can define the name of the large pool by passing the following flag when run
 python3 configure_reclient.py --large_pool_name=<NAME_OF_LARGE_POOL>
 ```
 
-By default, these actions will use the default worker pool, same as other actions.
+Thus, large actions are run on the following pool:
+
+- If `--large_pool_name` is set, on the pool with the specified name.
+- If `--large_pool_name` is not set and `--default_pool_name` is set, on the pool with the specified
+    name.
+- If neither `--large_pool_name` nor `--default_pool_name` are set, on the remote's default pool,
+    i.e., the pool used when actions do not request being run on a specific pool.

configure_reclient.py

@@ -91,9 +91,17 @@ def parse_args():
         help='Prints out files modified.',
         action='store_true',
     )
+    parser.add_argument(
+        '--default_pool_name',
+        help=('The remote pool name to run actions on. If unspecified, uses '
+              ' the remote\'s default pool.'),
+        default='',
+    )
     parser.add_argument(
         '--large_pool_name',
-        help=('The remote pool name to run large actions on.'),
+        help=('The remote pool name to run large actions on. If unspecified, '
+              'uses the pool specified with --default_pool_name, or else the '
+              'remote\'s default pool.'),
         default='',
     )
 
@@ -270,6 +278,8 @@ def generate_rewrapper_cfg(self, tool, host_os):
             f'{Paths.script_dir}/{tool}/rewrapper_{host_os}.cfg',
         ]
 
+        if self.args.default_pool_name:
+            rewrapper_cfg['platform']['Pool'] = self.args.default_pool_name
         for source_cfg_path in source_cfg_paths:
             rewrapper_cfg = ReclientCfg.merge_cfg(rewrapper_cfg,
                                                   source_cfg_path)
@@ -302,6 +312,8 @@ def generate_rewrapper_large_cfg(self, tool, host_os):
         ]
         if self.args.large_pool_name:
             rewrapper_cfg['platform']['Pool'] = self.args.large_pool_name
+        elif self.args.default_pool_name:
+            rewrapper_cfg['platform']['Pool'] = self.args.default_pool_name
         for source_cfg_path in source_cfg_paths:
             rewrapper_cfg = ReclientCfg.merge_cfg(rewrapper_cfg,
                                                   source_cfg_path)