Replace FutureApiLevel with an ApiLevel.

Keeping the int constant around for now as FutureApiLevelInt because
it's still useful in places that haven't adopted ApiLevel yet for
testing if their non-ApiLevel API level is current or not.

Test: treehugger
Bug: http://b/154667674
Change-Id: I47a7012703f41fdeb56f91edf9c83afa93042deb
diff --git a/java/sdk.go b/java/sdk.go
index 5f8cb24..0d7341e 100644
--- a/java/sdk.go
+++ b/java/sdk.go
@@ -107,7 +107,7 @@
 
 const (
 	// special version number for a not-yet-frozen SDK
-	sdkVersionCurrent sdkVersion = sdkVersion(android.FutureApiLevel)
+	sdkVersionCurrent sdkVersion = sdkVersion(android.FutureApiLevelInt)
 	// special version number to be used for SDK specs where version number doesn't
 	// make sense, e.g. "none", "", etc.
 	sdkVersionNone sdkVersion = sdkVersion(0)