[8u20] Request for approval: 8030741: Inference: implement eager resolution of return types, consistent with JDK-8028800

[Vicente-Arturo Romero-Zaldivar]

Please approve the backport to 8u20 of this fix that applies cleanly to 
8udev repo:

jdk9 bug: https://bugs.openjdk.java.net/browse/JDK-8030741
backport: https://bugs.openjdk.java.net/browse/JDK-8031534
changeset: http://hg.openjdk.java.net/jdk9/dev/langtools/rev/c062c8dc1e4a

reviewers: Dan Smith, Jonathan Gibbons

Thanks,
Vicente