Fix UAP in blink::ManifestManager's mojo binding

This CL resets own mojo binding in the internal function
of ManifestManager::ContextDestroyed because Blink's GC objects
that own mojo bindings manually need to reset the bindings to prevent
use after poison issue.

Bug: 979621
Change-Id: I38c4c3b532111f9ff721ef75b98d9e33a3f96441
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1705580Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: Miyoung Shin <myid.shin@igalia.com>
Cr-Commit-Position: refs/heads/master@{#678512}

third_party/blink/renderer/modules/manifest/manifest_manager.cc

@@ -267,6 +267,8 @@ void ManifestManager::Dispose() {
   // will be aware of the RenderFrame dying and should act on that. Consumers
   // in the renderer process should be correctly notified.
   ResolveCallbacks(ResolveStateFailure);
+
+  bindings_.CloseAllBindings();
 }
 
 void ManifestManager::Trace(blink::Visitor* visitor) {