wasm test suite (#1116)

* wasm: add test suite using headlless chrome

tests/wasm/testdata/event.go

@@ -0,0 +1,31 @@
+package main
+
+import "syscall/js"
+
+func main() {
+
+	ch := make(chan bool, 1)
+
+	println("1")
+
+	js.Global().
+		Get("document").
+		Call("querySelector", "#main").
+		Set("innerHTML", `<button id="testbtn">Test</button>`)
+
+	js.Global().
+		Get("document").
+		Call("querySelector", "#testbtn").
+		Call("addEventListener", "click",
+			js.FuncOf(func(this js.Value, args []js.Value) interface{} {
+				println("2")
+				ch <- true
+				println("3")
+				return nil
+			}))
+
+	println("4")
+	v := <-ch
+	println(v)
+
+}