Bug 1449756 - Make DisplayPort suppression PresShell specific and not process global. r=kats

Originally, DisplayPort suppression was a process-global static. This change makes it possible
to control DisplayPort suppression on a per-PresShell basis.

Differential Revision: https://phabricator.services.mozilla.com/D1759

layout/base/PresShell.cpp

@@ -809,6 +809,7 @@ PresShell::PresShell()
   , mLastCallbackEventRequest(nullptr)
   , mLastReflowStart(0.0)
   , mLastAnchorScrollPositionY(0)
+  , mActiveSuppressDisplayport(0)
   , mAPZFocusSequenceNumber(0)
   , mDocumentLoading(false)
   , mIgnoreFrameDestruction(false)
@@ -8555,6 +8556,47 @@ PresShell::IsVisible()
   return frame->IsVisibleConsideringAncestors(nsIFrame::VISIBILITY_CROSS_CHROME_CONTENT_BOUNDARY);
 }
 
+void
+PresShell::SuppressDisplayport(bool aEnabled)
+{
+  if (aEnabled) {
+    mActiveSuppressDisplayport++;
+  } else {
+    bool isSuppressed = IsDisplayportSuppressed();
+    mActiveSuppressDisplayport--;
+    if (isSuppressed && !IsDisplayportSuppressed()) {
+      // We unsuppressed the displayport, trigger a paint
+      if (nsIFrame* rootFrame = mFrameConstructor->GetRootFrame()) {
+        rootFrame->SchedulePaint();
+      }
+    }
+  }
+
+  MOZ_ASSERT(mActiveSuppressDisplayport >= 0);
+}
+
+static bool sDisplayPortSuppressionRespected = true;
+
+void
+PresShell::RespectDisplayportSuppression(bool aEnabled)
+{
+  bool isSuppressed = IsDisplayportSuppressed();
+  sDisplayPortSuppressionRespected = aEnabled;
+  if (isSuppressed && !IsDisplayportSuppressed()) {
+    // We unsuppressed the displayport, trigger a paint
+    if (nsIFrame* rootFrame = mFrameConstructor->GetRootFrame()) {
+      rootFrame->SchedulePaint();
+    }
+  }
+}
+
+bool
+PresShell::IsDisplayportSuppressed()
+{
+  return sDisplayPortSuppressionRespected &&
+         mActiveSuppressDisplayport > 0;
+}
+
 nsresult
 PresShell::GetAgentStyleSheets(nsTArray<RefPtr<StyleSheet>>& aSheets)
 {