Change name back to CreateJavaInputStreamAdaptor.

In order to fix open source builds, change WrapJavaInputStream's
name back to CreateJavaInputStreamAdaptor.

Remove FIXME in CopyJavaInputStream, and return a more generic type,
since the more specific type was only needed by a change in external/webkit,
which is being reverted since it depends on unreleased code.

Change-Id: I89b0431e357b509a2a0c17a624b31bd49d29070f