make NewAllocator's cancel func block on Wait

This way, the simple examples and tests don't need to do that
separately. Practically all users will want this cleanup work to be
synchronous, and practically all Go APIs are synchronous by default, so
this makes chromedp easier to use.

allocate.go

@@ -22,8 +22,12 @@ type Allocator interface {
 	// as temporary directories) will be freed.
 	Allocate(context.Context) (*Browser, error)
 
-	// Wait can be called after cancelling an allocator's context, to block
+	// TODO: Wait should probably return an error, which can then be
-	// until all of its resources have been freed.
+	// retrieved by the user if just calling cancel().
+
+	// Wait blocks until an allocator has freed all of its resources.
+	// Cancelling the context obtained via NewAllocator will already perform
+	// this operation, so normally there's no need to call Wait directly.
 	Wait()
 }
 
@@ -38,7 +42,11 @@ func NewAllocator(parent context.Context, opts ...AllocatorOption) (context.Cont
 	}
 
 	ctx = context.WithValue(ctx, contextKey{}, c)
-	return ctx, cancel
+	cancelWait := func() {
+		cancel()
+		c.Allocator.Wait()
+	}
+	return ctx, cancelWait
 }
 
 // AllocatorOption is a allocator option.

allocate_test.go

@@ -30,17 +30,14 @@ func TestExecAllocator(t *testing.T) {
 		t.Fatalf("wanted %q, got %q", want, got)
 	}
 
+	// TODO: make cancel() work here too
+	poolCancel()
+
 	tempDir := FromContext(taskCtx).Browser.userDataDir
-	pool := FromContext(taskCtx).Allocator
+	if _, err := os.Lstat(tempDir); !os.IsNotExist(err) {
-
-	cancel()
-	pool.Wait()
-
-	if _, err := os.Lstat(tempDir); os.IsNotExist(err) {
-		return
-	}
 		t.Fatalf("temporary user data dir %q not deleted", tempDir)
 	}
+}
 
 func TestExecAllocatorCancelParent(t *testing.T) {
 	t.Parallel()
@@ -56,15 +53,11 @@ func TestExecAllocatorCancelParent(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	tempDir := FromContext(taskCtx).Browser.userDataDir
-	pool := FromContext(taskCtx).Allocator
-
 	// Canceling the pool context should stop all browsers too.
 	poolCancel()
-	pool.Wait()
 
-	if _, err := os.Lstat(tempDir); os.IsNotExist(err) {
+	tempDir := FromContext(taskCtx).Browser.userDataDir
-		return
+	if _, err := os.Lstat(tempDir); !os.IsNotExist(err) {
-	}
 		t.Fatalf("temporary user data dir %q not deleted", tempDir)
 	}
+}

chromedp_test.go

@@ -64,6 +64,5 @@ func TestMain(m *testing.M) {
 	code := m.Run()
 
 	cancel()
-	FromContext(allocCtx).Allocator.Wait()
 	os.Exit(code)
 }

example_test.go

@@ -26,10 +26,6 @@ func ExampleTitle() {
 
 	fmt.Println(title)
 
-	// wait for the resources to be cleaned up
-	cancel()
-	chromedp.FromContext(ctx).Allocator.Wait()
-
 	// no expected output, to not run this test as part of 'go test'; it's
 	// too slow, requiring internet access.
 }
@@ -69,10 +65,6 @@ func ExampleExecAllocator() {
 	lines := bytes.Split(bs, []byte("\n"))
 	fmt.Printf("DevToolsActivePort has %d lines\n", len(lines))
 
-	// wait for the resources to be cleaned up
-	cancel()
-	chromedp.FromContext(allocCtx).Allocator.Wait()
-
 	// Output:
 	// DevToolsActivePort has 2 lines
 }
@@ -101,10 +93,6 @@ func ExampleNewContext_manyTabs() {
 	fmt.Printf("Same browser: %t\n", c1.Browser == c2.Browser)
 	fmt.Printf("Same tab: %t\n", c1.Target == c2.Target)
 
-	// wait for the resources to be cleaned up
-	cancel()
-	c1.Allocator.Wait()
-
 	// Output:
 	// Same browser: true
 	// Same tab: false

input_test.go

@@ -9,15 +9,13 @@ import (
 	"github.com/chromedp/cdproto/input"
 )
 
-const (
 // inViewportJS is a javascript snippet that will get the specified node
 // position relative to the viewport and returns true if the specified node
 // is within the window's viewport.
-	inViewportJS = `(function(a) {
+const inViewportJS = `(function(a) {
 		var r = a[0].getBoundingClientRect();
 		return r.top >= 0 && r.left >= 0 && r.bottom <= window.innerHeight && r.right <= window.innerWidth;
 	})($x('%s'))`
-)
 
 func TestMouseClickXY(t *testing.T) {
 	t.Parallel()