http2: add newly dialed conns to the pool before signaling completion

In dialCall.dial, close the done channel to mark dial completion after
adding the new connection to the clientConnPool.

Fixes a race condition in TestTransportBodyReadError, where the client
side of the test could observe the clientConnPool as unexpectedly
containing no conns, because the new conn had not yet been added to
the pool.

Fixes golang/go#44304.

Change-Id: I121200f9aa664fae29d0532e7fa2da47de3fe6a8
Reviewed-on: https://go-review.googlesource.com/c/net/+/410934
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Damien Neil <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: neild

http2/client_conn_pool.go

@@ -139,14 +139,15 @@ func (p *clientConnPool) getStartDialLocked(ctx context.Context, addr string) *d
 func (c *dialCall) dial(ctx context.Context, addr string) {
 	const singleUse = false // shared conn
 	c.res, c.err = c.p.t.dialClientConn(ctx, addr, singleUse)
-	close(c.done)
 
 	c.p.mu.Lock()
 	delete(c.p.dialing, addr)
 	if c.err == nil {
 		c.p.addConnLocked(addr, c.res)
 	}
 	c.p.mu.Unlock()
+
+	close(c.done)
 }
 
 // addConnIfNeeded makes a NewClientConn out of c if a connection for key doesn't