Fix a cts crash around proxy class fields.

org.apache.harmony.tests.java.io.SerializationStressTest4#test_writeObject_Proxy

As the static fields of proxy classes share the dex file indices, they
shouldn't be resolved in the dex cache or else Field::GetArtField()
may return a wrong art field that belong to a different proxy class.

(cherry pick commit a56ce5e2)

Bug: 20557050

Change-Id: If672c0e67bc49e672e34d75ffbe29c65f5a423b9