Fix toolchain definitions for bazel 0.17.1

Without this change, building fails with:

  $ bazel build tools:error_prone_warnings_toolchain
  ERROR: /usr/local/google/home/dborowitz/nobackup/c/gerrit-upstream/gerrit/tools/BUILD:45:1: no such target '@bazel_tools//tools/jdk:platformclasspath.jar': target 'platformclasspath.jar' not declared in package 'tools/jdk' (did you mean 'platformclasspath8.jar'?) defined by /usr/local/google/home/dborowitz/.cache/bazel/_bazel_`

This target was renamed in 0.17.1:

  https://bazel.googlesource.com/bazel/+/3987300d6651cf0e6e91b395696afac6913a7d66
  https://bazel.googlesource.com/bazel/+/35eaec4caae64af9077e7e614edfa62a09c3b0c4/CHANGELOG.md#release-0_17_1-2018_09_14

Change-Id: Ib1ade4041ecf3839e2755c21858882dca9dd30cb
diff --git a/tools/BUILD b/tools/BUILD
index cd34fe9..a2561ad 100644
--- a/tools/BUILD
+++ b/tools/BUILD
@@ -1,4 +1,8 @@
-load("@bazel_tools//tools/jdk:default_java_toolchain.bzl", "default_java_toolchain")
+load(
+    "@bazel_tools//tools/jdk:default_java_toolchain.bzl",
+    "JDK9_JVM_OPTS",
+    "default_java_toolchain",
+)
 
 py_binary(
     name = "merge_jars",
@@ -7,44 +11,10 @@
     visibility = ["//visibility:public"],
 )
 
-# TODO(davido): remove this when minimum suported Bazel version >= 0.17
-# Copied from tools/jdk/default_java_toolchain.bzl to make Bazel 0.16
-# and later Bazel released to work as expected. See this issue for context:
-# https://github.com/bazelbuild/bazel/issues/6009
-JDK9_JVM_OPTS = [
-    # Allow JavaBuilder to access internal javac APIs.
-    "--add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED",
-    "--add-exports=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED",
-    "--add-exports=jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED",
-    "--add-exports=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED",
-    "--add-exports=jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED",
-    "--add-exports=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED",
-    "--add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED",
-    "--add-opens=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED",
-
-    # override the javac in the JDK.
-    "--patch-module=java.compiler=$(location @bazel_tools//third_party/java/jdk/langtools:java_compiler_jar)",
-    "--patch-module=jdk.compiler=$(location @bazel_tools//third_party/java/jdk/langtools:jdk_compiler_jar)",
-
-    # quiet warnings from com.google.protobuf.UnsafeUtil,
-    # see: https://github.com/google/protobuf/issues/3781
-    "--add-opens=java.base/java.nio=ALL-UNNAMED",
-]
-
-# See https://github.com/bazelbuild/bazel/issues/3427 for more context
-default_java_toolchain(
-    name = "error_prone_warnings_toolchain_bazel_0.16",
-    bootclasspath = ["@bazel_tools//tools/jdk:platformclasspath.jar"],
-    jvm_opts = JDK9_JVM_OPTS,
-    package_configuration = [
-        ":error_prone",
-    ],
-    visibility = ["//visibility:public"],
-)
-
 default_java_toolchain(
     name = "error_prone_warnings_toolchain",
-    bootclasspath = ["@bazel_tools//tools/jdk:platformclasspath.jar"],
+    bootclasspath = ["@bazel_tools//tools/jdk:platformclasspath9.jar"],
+    jvm_opts = JDK9_JVM_OPTS,
     package_configuration = [
         ":error_prone",
     ],