Browser viewer: Try using document.execCommand to copy since it works on non-secure origins as well

src/pyj/read_book/iframe.pyj

@@ -871,6 +871,13 @@ class IframeBoss:
             select_crw(crw)
 
     def copy_selection(self):
+        if not runtime.is_standalone_viewer:
+            try:
+                if document.execCommand('copy'):
+                    return
+            except:
+                pass
+
         s = window.getSelection()
         text = s.toString()
         if text:

src/pyj/read_book/ui.pyj

@@ -84,6 +84,29 @@ class ReadUI:
         ui_operations.open_url = def(url):
             window.open(url, '_blank')
         ui_operations.copy_selection = def(text, html):
+            if not html:
+                # try using document.execCommand which on chrome allows the
+                # copy on non-secure origin if this is close to a user
+                # interaction event
+                active_elem = document.activeElement
+                ta = document.createElement("textarea")
+                ta.value = text
+                ta.style.position = 'absolute'
+                ta.style.top = window.innerHeight + 'px'
+                ta.style.left = window.innerWidth + 'px'
+                document.body.appendChild(ta)
+                ta.focus()
+                ta.select()
+                ok = False
+                try:
+                    ok = document.execCommand('copy')
+                except:
+                    pass
+                document.body.removeChild(ta)
+                if active_elem:
+                    active_elem.focus()
+                if ok:
+                    return
             if not window.navigator.clipboard:
                 return error_dialog(_('No clipboard access'), _(
                     'Your browser requires you to access the Content server over an HTTPS connection'