Add providers support

Propagate the providers methods from
https://github.com/google/blueprint/pull/309 to Soong.

Test: m checkbuild
Change-Id: Iad7a9023df4421cd01dbb0518be0e85382097481

android/mutator.go

@@ -315,6 +315,14 @@ type BottomUpMutatorContext interface {
 	// be used to add dependencies on the toVariationName variant using the fromVariationName
 	// variant.
 	CreateAliasVariation(fromVariationName, toVariationName string)
+
+	// SetVariationProvider sets the value for a provider for the given newly created variant of
+	// the current module, i.e. one of the Modules returned by CreateVariations..  It panics if
+	// not called during the appropriate mutator or GenerateBuildActions pass for the provider,
+	// if the value is not of the appropriate type, or if the module is not a newly created
+	// variant of the current module.  The value should not be modified after being passed to
+	// SetVariationProvider.
+	SetVariationProvider(module blueprint.Module, provider blueprint.ProviderKey, value interface{})
 }
 
 type bottomUpMutatorContext struct {
@@ -550,3 +558,7 @@ func (b *bottomUpMutatorContext) AliasVariation(variationName string) {
 func (b *bottomUpMutatorContext) CreateAliasVariation(fromVariationName, toVariationName string) {
 	b.bp.CreateAliasVariation(fromVariationName, toVariationName)
 }
+
+func (b *bottomUpMutatorContext) SetVariationProvider(module blueprint.Module, provider blueprint.ProviderKey, value interface{}) {
+	b.bp.SetVariationProvider(module, provider, value)
+}