Bug 1883435 - Don't include GleanMetrics.h from Document.h. r=chutten,necko-reviewers,valentin

In bug 1883435 comment 2 chutten mentions that including
nsGlobalWindowInner.h from GleanMetrics.h causes a stylo build failure.

This is because nsGlobalWindowInner.h itself brings a bunch of DOM
bindings template soup that bindgen isn't great at dealing with.

That can be fixed in various ways. However, there is a simpler fix,
which is not including GleanMetrics at all.

It's trivial to do, and given it's a massive autogenerated file, and
Document.h is a very common header, it's worth doing this if only for
build times.

Fix a bunch of unused includes while at it.

Differential Revision: https://phabricator.services.mozilla.com/D203625

dom/html/HTMLMediaElement.cpp

@@ -51,6 +51,7 @@
 #include "base/basictypes.h"
 #include "jsapi.h"
 #include "js/PropertyAndElement.h"  // JS_DefineProperty
+#include "mozilla/AppShutdown.h"
 #include "mozilla/ArrayUtils.h"
 #include "mozilla/AsyncEventDispatcher.h"
 #include "mozilla/EMEUtils.h"