net/http: remove use of DeepEqual for testing errors

Comparing errors using DeepEqual breaks if frame information
is added as proposed in Issue #29934.

Updates #29934.

Change-Id: I4ef076e262109a9d6f5b18846129df2535611d71
Reviewed-on: https://go-review.googlesource.com/c/162178
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>

src/net/http/clientserver_test.go

@@ -560,7 +560,7 @@ func testCancelRequestMidBody(t *testing.T, h2 bool) {
 	if all != "Hello" {
 		t.Errorf("Read %q (%q + %q); want Hello", all, firstRead, rest)
 	}
-	if !reflect.DeepEqual(err, ExportErrRequestCanceled) {
+	if err != ExportErrRequestCanceled {
 		t.Errorf("ReadAll error = %v; want %v", err, ExportErrRequestCanceled)
 	}
 }

src/net/http/transport.go

@@ -2073,7 +2073,10 @@ func (e *httpError) Timeout() bool   { return e.timeout }
 func (e *httpError) Temporary() bool { return true }
 
 var errTimeout error = &httpError{err: "net/http: timeout awaiting response headers", timeout: true}
-var errRequestCanceled = errors.New("net/http: request canceled")
+
+// errRequestCanceled is set to be identical to the one from h2 to facilitate
+// testing.
+var errRequestCanceled = http2errRequestCanceled
 var errRequestCanceledConn = errors.New("net/http: request canceled while waiting for connection") // TODO: unify?
 
 func nop() {}