Bug 1590639 part 6: Fix non-unified build issues in layout/inspector. r=emilio

This patch:
- Gives ServoStyleRuleMap.cpp an include for Element.h (to provide that type).
- Gives inDeepTreeWalker.cpp a mozilla::dom prefix for its one use of Document.
- Gives inLayoutUtils.cpp a "using" decl for mozilla::dom, so we can compile
  with the many un-namespaced "Document" and "Element" usages in that file.

Depends on D50167

Differential Revision: https://phabricator.services.mozilla.com/D50168

--HG--
extra : moz-landing-system : lando

layout/inspector/ServoStyleRuleMap.cpp

@@ -11,6 +11,7 @@
 #include "mozilla/dom/CSSRuleBinding.h"
 #include "mozilla/dom/CSSStyleRule.h"
 #include "mozilla/dom/Document.h"
+#include "mozilla/dom/Element.h"
 #include "mozilla/dom/ShadowRoot.h"
 #include "mozilla/IntegerRange.h"
 #include "mozilla/ServoStyleSet.h"

layout/inspector/inDeepTreeWalker.cpp

@@ -144,7 +144,7 @@ static already_AddRefed<nsINodeList> GetChildren(nsINode* aParent,
 
   nsCOMPtr<nsINodeList> ret;
   if (aShowSubDocuments) {
-    Document* domdoc = inLayoutUtils::GetSubDocumentFor(aParent);
+    mozilla::dom::Document* domdoc = inLayoutUtils::GetSubDocumentFor(aParent);
     if (domdoc) {
       aParent = domdoc;
     }

layout/inspector/inLayoutUtils.cpp

@@ -17,6 +17,7 @@
 #include "mozilla/dom/Element.h"
 
 using namespace mozilla;
+using namespace mozilla::dom;
 
 ///////////////////////////////////////////////////////////////////////////////