Add providers support

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

Test: m checkbuild
Change-Id: Iad7a9023df4421cd01dbb0518be0e85382097481
diff --git a/android/singleton.go b/android/singleton.go
index 2c51c6c..9832378 100644
--- a/android/singleton.go
+++ b/android/singleton.go
@@ -29,6 +29,16 @@
 	ModuleType(module blueprint.Module) string
 	BlueprintFile(module blueprint.Module) string
 
+	// ModuleProvider returns the value, if any, for the provider for a module.  If the value for the
+	// provider was not set it returns the zero value of the type of the provider, which means the
+	// return value can always be type-asserted to the type of the provider.  The return value should
+	// always be considered read-only.  It panics if called before the appropriate mutator or
+	// GenerateBuildActions pass for the provider on the module.
+	ModuleProvider(module blueprint.Module, provider blueprint.ProviderKey) interface{}
+
+	// ModuleHasProvider returns true if the provider for the given module has been set.
+	ModuleHasProvider(module blueprint.Module, provider blueprint.ProviderKey) bool
+
 	ModuleErrorf(module blueprint.Module, format string, args ...interface{})
 	Errorf(format string, args ...interface{})
 	Failed() bool