bazel: Move auto-value dep to external_plugin_deps.bzl

This is the pattern expected with plugins providing standalone build
support.

Change-Id: I9dcea5be85731882a1b184b9d59fba33af2398e6

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 11075ae..66ad7d0 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -29,22 +29,6 @@
     yarn_lock = "//:yarn.lock",
 )
 
-load("//tools/bzl:maven_jar.bzl", "maven_jar")
-
-AUTO_VALUE_VERSION = "1.7.4"
-
-maven_jar(
-    name = "auto-value",
-    artifact = "com.google.auto.value:auto-value:" + AUTO_VALUE_VERSION,
-    sha1 = "6b126cb218af768339e4d6e95a9b0ae41f74e73d",
-)
-
-maven_jar(
-    name = "auto-value-annotations",
-    artifact = "com.google.auto.value:auto-value-annotations:" + AUTO_VALUE_VERSION,
-    sha1 = "eff48ed53995db2dadf0456426cc1f8700136f86",
-)
-
 # Load plugin API
 load(
     "@com_googlesource_gerrit_bazlets//:gerrit_api.bzl",
@@ -53,3 +37,7 @@
 
 # Release Plugin API
 gerrit_api()
+
+load("//:external_plugin_deps.bzl", "external_plugin_deps")
+
+external_plugin_deps()

external_plugin_deps.bzl

diff --git a/external_plugin_deps.bzl b/external_plugin_deps.bzl
new file mode 100644
index 0000000..fdf9c1c
--- /dev/null
+++ b/external_plugin_deps.bzl
@@ -0,0 +1,16 @@
+load("@bazel_tools//tools/build_defs/repo:maven_rules.bzl", "maven_jar")
+
+def external_plugin_deps():
+    AUTO_VALUE_VERSION = "1.7.4"
+
+    maven_jar(
+        name = "auto-value",
+        artifact = "com.google.auto.value:auto-value:" + AUTO_VALUE_VERSION,
+        sha1 = "6b126cb218af768339e4d6e95a9b0ae41f74e73d",
+    )
+
+    maven_jar(
+        name = "auto-value-annotations",
+        artifact = "com.google.auto.value:auto-value-annotations:" + AUTO_VALUE_VERSION,
+        sha1 = "eff48ed53995db2dadf0456426cc1f8700136f86",
+    )