diff --git BUILD.gn BUILD.gn
index d6969b427ed614ec861c338cdd127ba4717dad1d..c6b7c034aea8f2d58c5bb0e4c5590cc1d27f9f5d 100644
--- BUILD.gn
+++ BUILD.gn
@@ -97,6 +97,9 @@ declare_args() {
   install_prefix = ""
 
   angle_use_crypto_hasher = build_with_chromium
+
+  angle_commit_id = ""
+  angle_commit_position = "0"
 }
 
 declare_args() {
@@ -956,6 +959,8 @@ action("angle_commit_id") {
     "gen",
     rebase_path(_commit_id_header, root_build_dir),
     rebase_path(depfile, root_build_dir),
+    angle_commit_position,
+    angle_commit_id,
   ]
 
   public_configs = [ ":angle_commit_id_config" ]
diff --git src/commit_id.py src/commit_id.py
index 5c28fe8184cbe5430f9253d1b2d6f59e787c1e6b..3a6f89f749fc2da3310ddc0806a486f9a8495864 100755
--- src/commit_id.py
+++ src/commit_id.py
@@ -13,7 +13,7 @@ import os
 
 usage = """\
 Usage: commit_id.py position               - print commit position
-       commit_id.py gen <output> [depfile] - generate commit.h"""
+       commit_id.py gen <output> [depfile] [commit_position] [commit_id] - generate commit.h"""
 
 
 def grab_output(command, cwd):
@@ -128,15 +128,24 @@ def main():
         sys.exit(usage)
 
     output_file = sys.argv[2]
-    depfile = sys.argv[3] if len(sys.argv) == 4 else None
+    depfile = sys.argv[3] if len(sys.argv) >= 4 else None
     commit_id_size = 12
     commit_date = 'unknown date'
     commit_position = '0'
 
+    if len(sys.argv) >= 5:
+      commit_position = sys.argv[4]
+      assert commit_position.isnumeric(), commit_position
+
+    commit_id = None
+    if len(sys.argv) >= 6 and len(sys.argv[5]) > 0:
+      commit_id = sys.argv[5]
+      assert len(commit_id) == commit_id_size, commit_id
+
     # If the ANGLE_UPSTREAM_HASH environment variable is set, use it as
     # commit_id. commit_date will be 'unknown date' and commit_position will be 0
     # in this case. See details in roll_aosp.sh where commit_id.py is invoked.
-    commit_id = os.environ.get('ANGLE_UPSTREAM_HASH')
+    commit_id = os.environ.get('ANGLE_UPSTREAM_HASH', commit_id)
     # If ANGLE_UPSTREAM_HASH environment variable is not set, use the git command
     # to get the git hash, when .git is available
     if git_dir_exists and not commit_id: