Initial kotlin support

Allow java libraries to specify .kt sources, precompile them with
kotlin, and then pass them in the classpath to javac.

Bug: 65219535
Test: java_test.go
Change-Id: Ife22b6ef82ced9ec26a9e5392b2dadacbb16546f

java/config/kotlin.go

@@ -0,0 +1,25 @@
+// Copyright 2017 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package config
+
+var (
+	KotlinStdlibJar = "external/kotlinc/lib/kotlin-stdlib.jar"
+)
+
+func init() {
+	pctx.SourcePathVariable("KotlincCmd", "external/kotlinc/bin/kotlinc")
+	pctx.SourcePathVariable("KotlinCompilerJar", "external/kotlinc/lib/kotlin-compiler.jar")
+	pctx.SourcePathVariable("KotlinStdlibJar", KotlinStdlibJar)
+}