static/frontend/unit: update page titles for unit tabs

The tab page titles are updated as follows:
  <unit name> {package,module,directory} <tab name>

Change-Id: Ifc13660ca83b86adfa96c4d8810e26b8ab59310b
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/345350
Trust: Jamal Carvalho <jamal@golang.org>
Run-TryBot: Jamal Carvalho <jamal@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Julie Qiu <julie@golang.org>
diff --git a/static/frontend/unit/unit.tmpl b/static/frontend/unit/unit.tmpl
index fdbc458..a4adfd2 100644
--- a/static/frontend/unit/unit.tmpl
+++ b/static/frontend/unit/unit.tmpl
@@ -4,7 +4,11 @@
   license that can be found in the LICENSE file.
 -->
 
-{{define "title"}}<title>{{.Title}} {{if ne .PageType "std"}}{{.PageType}} - {{.Unit.Path}}{{end}} - pkg.go.dev</title>{{end}}
+{{define "title"}}
+  <title>
+    {{.Title}} {{if ne .PageType "std"}}{{.PageType}}{{end}} {{.SelectedTab.Name}} {{if ne .PageType "std"}} - {{.Unit.Path}}{{end}} - pkg.go.dev
+  </title>
+{{end}}
 
 {{define "description"}}{{.MetaDescription}}{{end}}