Pass request context to frame observer

This allows the frame observer to access the context passed to
gocql.

conn.go

@@ -788,6 +788,7 @@ func (c *Conn) recv(ctx context.Context) error {
 	} else if head.stream != call.streamID {
 		panic(fmt.Sprintf("call has incorrect streamID: got %d expected %d", call.streamID, head.stream))
 	}
+	parseObserver.reqCtx = call.reqCtx
 
 	framer := newFramer(c.compressor, c.version)
 
@@ -851,6 +852,9 @@ type callReq struct {
 	// streamObserverEndOnce ensures that either StreamAbandoned or StreamFinished is called,
 	// but not both.
 	streamObserverEndOnce sync.Once
+
+	// context passed to execute.
+	reqCtx context.Context
 }
 
 type callResp struct {
@@ -1104,6 +1108,7 @@ func (c *Conn) exec(ctx context.Context, req frameBuilder, tracer Tracer) (*fram
 		timeout:  make(chan struct{}),
 		streamID: stream,
 		resp:     make(chan callResp),
+		reqCtx:   ctx,
 	}
 
 	if c.streamObserver != nil {

frame.go

@@ -410,6 +410,7 @@ type framer struct {
 type frameParseObserver struct {
 	head          ObservedFrameHeader
 	frameObserver FrameObserver
+	reqCtx        context.Context
 }
 
 func (fpo *frameParseObserver) observeFrame(ff *framer, f frame) {
@@ -425,7 +426,11 @@ func (fpo *frameParseObserver) observeFrame(ff *framer, f frame) {
 		of.RowCount = rows.numRows
 		of.RowsSize = rows.rowsContentSize
 	}
-	fpo.frameObserver.ObserveFrame(context.TODO(), of)
+	ctx := fpo.reqCtx
+	if ctx == nil {
+		ctx = context.TODO()
+	}
+	fpo.frameObserver.ObserveFrame(ctx, of)
 }
 
 func newFramer(compressor Compressor, version byte) *framer {