[idlharness.js] Add main interface as dep for implements

Case was revealed by https://github.com/web-platform-tests/wpt/pull/9794
Specifically, Navigator implements NavigatorUserMedia;

Navigator was not being added as a depenedency, and thus was not being imported.

Change-Id: I07436c561bb0b567a431393a20f6a179ef5b364b
Reviewed-on: https://chromium-review.googlesource.com/1104707Reviewed-by: Robert Ma <robertma@chromium.org>
Commit-Queue: Luke Bj <lukebjerring@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568143}

third_party/WebKit/LayoutTests/external/wpt/resources/idlharness.js

@@ -257,7 +257,10 @@ IdlArray.prototype.add_dependency_idls = function(raw_idls, options)
 
     const all_deps = new Set();
     Object.values(this.inheritance).forEach(v => all_deps.add(v));
-    Object.values(this.implements).forEach(v => all_deps.add(v));
+    Object.entries(this.implements).forEach(([k, v]) => {
+        all_deps.add(k);
+        all_deps.add(v);
+    });
     // NOTE: If 'A includes B' for B that we care about, then A is also a dep.
     Object.keys(this.includes).forEach(k => {
         all_deps.add(k);