Add AliasVariation to BottomUpMutatorContext.

Test: TreeHugger
Change-Id: Ib9c5db8f671ed8f0742183fc533dcc582269d17a
diff --git a/android/mutator.go b/android/mutator.go
index 4a5338f..df68726 100644
--- a/android/mutator.go
+++ b/android/mutator.go
@@ -151,6 +151,7 @@
 	AddFarVariationDependencies([]blueprint.Variation, blueprint.DependencyTag, ...string)
 	AddInterVariantDependency(tag blueprint.DependencyTag, from, to blueprint.Module)
 	ReplaceDependencies(string)
+	AliasVariation(variationName string)
 }
 
 type bottomUpMutatorContext struct {
@@ -335,3 +336,7 @@
 func (b *bottomUpMutatorContext) ReplaceDependencies(name string) {
 	b.bp.ReplaceDependencies(name)
 }
+
+func (b *bottomUpMutatorContext) AliasVariation(variationName string) {
+	b.bp.AliasVariation(variationName)
+}