Revert "Revert "Include proguard flag files from transitive java_library deps""

This reverts commit 6f7e288fb5.

Reason for revert: Downstream proguard usage has been fixed.

Change-Id: I3667e7e908eebc62c640b42cb96b04993fc66e45

java/java.go

@@ -294,6 +294,11 @@ type UsesLibraryDependency interface {
 	ClassLoaderContexts() dexpreopt.ClassLoaderContextMap
 }
 
+// Provides transitive Proguard flag files to downstream DEX jars.
+type LibraryDependency interface {
+	ExportedProguardFlagFiles() android.Paths
+}
+
 // TODO(jungjw): Move this to kythe.go once it's created.
 type xref interface {
 	XrefJavaFiles() android.Paths
@@ -596,9 +601,17 @@ func normalizeJavaVersion(ctx android.BaseModuleContext, javaVersion string) jav
 type Library struct {
 	Module
 
+	exportedProguardFlagFiles android.Paths
+
 	InstallMixin func(ctx android.ModuleContext, installPath android.Path) (extraInstallDeps android.Paths)
 }
 
+var _ LibraryDependency = (*Library)(nil)
+
+func (j *Library) ExportedProguardFlagFiles() android.Paths {
+	return j.exportedProguardFlagFiles
+}
+
 var _ android.ApexModule = (*Library)(nil)
 
 // Provides access to the list of permitted packages from apex boot jars.
@@ -694,6 +707,15 @@ func (j *Library) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 		}
 		j.installFile = ctx.InstallFile(installDir, j.Stem()+".jar", j.outputFile, extraInstallDeps...)
 	}
+
+	j.exportedProguardFlagFiles = append(j.exportedProguardFlagFiles,
+		android.PathsForModuleSrc(ctx, j.dexProperties.Optimize.Proguard_flags_files)...)
+	ctx.VisitDirectDeps(func(m android.Module) {
+		if lib, ok := m.(LibraryDependency); ok && ctx.OtherModuleDependencyTag(m) == staticLibTag {
+			j.exportedProguardFlagFiles = append(j.exportedProguardFlagFiles, lib.ExportedProguardFlagFiles()...)
+		}
+	})
+	j.exportedProguardFlagFiles = android.FirstUniquePaths(j.exportedProguardFlagFiles)
 }
 
 func (j *Library) DepsMutator(ctx android.BottomUpMutatorContext) {