Add logtags source file support

Add support for converting logtags files to source files.  Each
.logtags file is converted to a .java file, but only after all
.logtags files have been combined into a merged text file by
the logtagsSingleton.

Change-Id: I375d82874029bd26a7c528e46add2a638ba123f9

java/java.go

@@ -106,6 +106,8 @@ type javaBase struct {
 
 	exportAidlIncludeDirs []string
 
+	logtagsSrcs []string
+
 	// installed file for binary dependency
 	installFile string
 }
@@ -255,7 +257,7 @@ func (j *javaBase) GenerateJavaBuildActions(ctx common.AndroidModuleContext) {
 
 	srcFiles := common.ExpandSources(ctx, j.properties.Srcs)
 
-	srcFiles = genSources(ctx, srcFiles, flags)
+	srcFiles = j.genSources(ctx, srcFiles, flags)
 
 	if len(srcFiles) > 0 {
 		// Compile java sources into .class files
@@ -360,6 +362,12 @@ func (j *javaBase) AidlPreprocessed() string {
 	return ""
 }
 
+var _ logtagsProducer = (*javaBase)(nil)
+
+func (j *javaBase) logtags() []string {
+	return j.logtagsSrcs
+}
+
 //
 // Java libraries (.jar file)
 //