Fix ChromeOS Swarming bot compile

BUG=skia:5158
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1886573004

Review URL: https://codereview.chromium.org/1886573004
diff --git a/platform_tools/chromeos/bin/chromeos_make b/platform_tools/chromeos/bin/chromeos_make
index a1cb2ba..cb58a9c 100755
--- a/platform_tools/chromeos/bin/chromeos_make
+++ b/platform_tools/chromeos/bin/chromeos_make
@@ -63,6 +63,12 @@
 # thinks we're in a Chrome checkout.
 echo "Delete me!" > "${CHROMEOS_CHROOT}/.gclient"
 
+# We may also need a .git directory.
+GIT_DIR="${CHROMEOS_CHROOT}/src/third_party/chromite/.git"
+if ! [[ -d "${GIT_DIR}" ]]; then
+  mkdir -p ${GIT_DIR}
+fi
+
 # Where the Skia code will pretend to live inside the chroot.
 SKIA_TOP_DIR="${SCRIPT_DIR}/../../.."