get back "WebDriver BiDi download started"

Author: sadym-chromium

index.bs

@@ -5592,6 +5592,40 @@ The [=remote end event trigger=] is the
 
 </div>
 
+<div algorithm>
+The [=remote end event trigger=] is the <dfn export>WebDriver BiDi download
+started</dfn> steps given |navigable| and |navigation status|:
+
+Issue: TODO: Removed after HTML spec switched to [=WebDriver BiDi download will begin=].
+
+1. Let |navigation info| be the result of [=get the navigation info=] given |navigable| and
+    |navigation status|.
+
+1. Let |params| be a [=/map=] matching the <code>browsingContext.DownloadWillBeginParams</code>
+   production, with the <code>context</code> field set to |navigation info|["<code>context</code>"],
+   the <code>navigation</code> field set to |navigation info|["<code>navigation</code>"], the
+   <code>timestamp</code> field set to |navigation info|["<code>timestamp</code>"], the
+   <code>url</code> field set to |navigation info|["<code>url</code>"] and
+   <code>suggestedFilename</code> field set to |navigation status|'s
+   <code>suggestedFilename</code>.
+
+1. Let |body| be a [=/map=] matching the
+   <code>browsingContext.DownloadWillBegin</code> production, with the
+   <code>params</code> field set to |params|.
+
+1. Let |navigation id| be |navigation status|'s id.
+
+1. Let |related navigables| be a [=/set=] containing |navigable|.
+
+1. [=Resume=] with "<code>download started</code>", |navigation id|, and |navigation status|.
+
+1. For each |session| in the [=set of sessions for which an event is enabled=]
+   given "<code>browsingContext.downloadWillBegin</code>" and |related navigables|:
+
+  1. [=Emit an event=] with |session| and |body|.
+
+</div>
+
 #### The browsingContext.downloadEnd Event #### {#event-browsingContext-downloadEnd}
 
 <dl>