Add an RBE setup script that developers can source to run RBE builds

Test: Ran "source build/envsetup.sh && source build/rbesetup.sh", then
ran "use_rbe m" and that worked.

Change-Id: I2413a3648e9b2ff680cab6fededc07bbdd43378f

rbesetup.sh

@@ -0,0 +1,25 @@
+source build/envsetup.sh
+
+# This function prefixes the given command with appropriate variables needed
+# for the build to be executed with RBE.
+function use_rbe() {
+  local RBE_LOG_DIR="/tmp"
+  local RBE_BINARIES_DIR="prebuilts/remoteexecution-client/latest/"
+  local DOCKER_IMAGE="gcr.io/androidbuild-re-dockerimage/android-build-remoteexec-image@sha256:582efb38f0c229ea39952fff9e132ccbe183e14869b39888010dacf56b360d62"
+
+  # Do not set an invocation-ID and let reproxy auto-generate one.
+  USE_RBE="true" \
+  FLAG_server_address="unix:///tmp/reproxy_$RANDOM.sock" \
+  FLAG_exec_root="$(gettop)" \
+  FLAG_platform="container-image=docker://${DOCKER_IMAGE}" \
+  RBE_use_application_default_credentials="true" \
+  RBE_log_dir="${RBE_LOG_DIR}" \
+  RBE_reproxy_wait_seconds="20" \
+  RBE_output_dir="${RBE_LOG_DIR}" \
+  RBE_log_path="text://${RBE_LOG_DIR}/reproxy_log.txt" \
+  RBE_CXX_EXEC_STRATEGY="remote_local_fallback" \
+  RBE_cpp_dependency_scanner_plugin="${RBE_BINARIES_DIR}/dependency_scanner_go_plugin.so" \
+  RBE_DIR=${RBE_BINARIES_DIR} \
+  RBE_re_proxy="${RBE_BINARIES_DIR}/reproxy" \
+  $@
+}