Added phony module type for soong.

The "required" field within "phony" module in .bp file has to be
non-empty. And "phony" module doesn't contain any "src" files.
Bug: b/32981153
Test: make -j out/soong/build.ninja

Change-Id: Iaa2009467c44702572b97ca9cbd02c1d368c8d83
diff --git a/phony/phony.go b/phony/phony.go
new file mode 100644
index 0000000..c405af8
--- /dev/null
+++ b/phony/phony.go
@@ -0,0 +1,63 @@
+// Copyright 2016 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 phony
+
+import (
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/google/blueprint"
+
+	"android/soong/android"
+)
+
+func init() {
+	android.RegisterModuleType("phony", phonyFactory)
+}
+
+type phony struct {
+	android.ModuleBase
+	requiredModuleNames []string
+}
+
+func phonyFactory() (blueprint.Module, []interface{}) {
+	module := &phony{}
+
+	return android.InitAndroidModule(module)
+}
+
+func (p *phony) DepsMutator(ctx android.BottomUpMutatorContext) {
+}
+
+func (p *phony) GenerateAndroidBuildActions(ctx android.ModuleContext) {
+	p.requiredModuleNames = ctx.RequiredModuleNames()
+	if len(p.requiredModuleNames) == 0 {
+		ctx.PropertyErrorf("required", "phony must not have empty required dependencies in order to be useful(and therefore permitted).")
+	}
+}
+
+func (p *phony) AndroidMk() (ret android.AndroidMkData, err error) {
+	ret.Custom = func(w io.Writer, name, prefix, moduleDir string) error {
+		fmt.Fprintln(w, "\ninclude $(CLEAR_VARS)")
+		fmt.Fprintln(w, "LOCAL_PATH :=", moduleDir)
+		fmt.Fprintln(w, "LOCAL_MODULE :=", name)
+		fmt.Fprintln(w, "LOCAL_REQUIRED_MODULES := "+strings.Join(p.requiredModuleNames, " "))
+		fmt.Fprintln(w, "include $(BUILD_PHONY_PACKAGE)")
+
+		return nil
+	}
+	return
+}