leak-detector: Remove InternalSettings supplement from Page

Internal settings are ScriptWrappable and thus may retain documents
depending on whether the garbage collector(s) are able to find the settings
object through the Page supplement.

Bug: 843903, 928781
Change-Id: I53458c6eb761a98ddc0e437174a233682e442586
Reviewed-on: https://chromium-review.googlesource.com/c/1456001Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629545}

third_party/blink/renderer/controller/BUILD.gn

@@ -18,6 +18,7 @@ jumbo_component("controller") {
   deps = [
     "//skia",
     "//third_party/blink/renderer/core",
+    "//third_party/blink/renderer/core:testing",
     "//third_party/blink/renderer/modules",
     "//third_party/blink/renderer/platform",
     "//v8",

third_party/blink/renderer/controller/blink_leak_detector.cc

@@ -15,6 +15,7 @@
 #include "third_party/blink/renderer/core/frame/local_frame.h"
 #include "third_party/blink/renderer/core/frame/web_local_frame_impl.h"
 #include "third_party/blink/renderer/core/page/page.h"
+#include "third_party/blink/renderer/core/testing/internal_settings.h"
 #include "third_party/blink/renderer/core/workers/dedicated_worker_messaging_proxy.h"
 #include "third_party/blink/renderer/core/workers/worker_thread.h"
 #include "third_party/blink/renderer/platform/bindings/v8_per_isolate_data.h"
@@ -65,6 +66,11 @@ void BlinkLeakDetector::PerformLeakDetection(
   for (auto resource_fetcher : ResourceFetcher::MainThreadFetchers())
     resource_fetcher->PrepareForLeakDetection();
 
+  // Internal settings are ScriptWrappable and thus may retain documents
+  // depending on whether the garbage collector(s) are able to find the settings
+  // object through the Page supplement.
+  InternalSettings::PrepareForLeakDetection();
+
   // Task queue may contain delayed object destruction tasks.
   // This method is called from navigation hook inside FrameLoader,
   // so previous document is still held by the loader until the next event loop.

third_party/blink/renderer/core/testing/internal_settings.cc

@@ -549,4 +549,12 @@ void InternalSettings::setAutoplayPolicy(const String& policy_str,
   GetSettings()->SetAutoplayPolicy(policy);
 }
 
+void InternalSettings::PrepareForLeakDetection() {
+  // Prepares for leak detection by removing all InternalSetting objects from
+  // Pages.
+  for (Page* page : Page::OrdinaryPages()) {
+    page->RemoveSupplement<InternalSettings>();
+  }
+}
+
 }  // namespace blink

third_party/blink/renderer/core/testing/internal_settings.h

@@ -51,6 +51,8 @@ class InternalSettings final : public InternalSettingsGenerated,
  public:
   static const char kSupplementName[];
 
+  static void PrepareForLeakDetection();
+
   class Backup {
     DISALLOW_NEW();