Interface update, per-method Contexts.

filter/txnBuf/context.go

Index: filter/txnBuf/context.go
diff --git a/filter/txnBuf/context.go b/filter/txnBuf/context.go
index 63e1cace82b81b63833ffe9208bca19b031892d7..b044328820e4a32b1c987f72c0e554b63831e732 100644
--- a/filter/txnBuf/context.go
+++ b/filter/txnBuf/context.go
@@ -45,17 +45,3 @@ func memoryCorruption(err error) {
 		panic(err)
 	}
 }
-
-// GetNoTxn allows you to to escape the buffered transaction (if any), and get
-// a non-transactional handle to the datastore. This does not invalidate the
-// currently-buffered transaction, but it also does not see any effects of it.
-//
-// TODO(iannucci): This is messy, but mostly because the way that transactions
-// work is messy. Fixing luci/gae#issues/23 would help though, because it means
-// we could make transactionality recorded by a single index in the context
-// instead of relying on function nesting.
-func GetNoTxn(c context.Context) ds.Interface {

[iannucci, 2016/09/16 01:01:13]

it's important that escaping the transaction via `datastore.WithTransaction(c,
nil)` also escapes the transaction buffer too.

[dnj, 2016/09/16 05:44:42]

I remember thinking about this, and for some reason I concluded that it was not
a problem, but it's been a few weeks and I don't remember specifically why. I'll
add the nilling back in.

-	c = context.WithValue(c, dsTxnBufParent, nil)
-	c = context.WithValue(c, dsTxnBufHaveLock, nil)
-	return ds.GetNoTxn(c)
-}