Bug 1662838 part 2: Remove nsIContentViewer's unused pausePainting() and resumePainting() APIs. r=tnikkel

These APIs are entirely unused (aside from one usage in a test, which part 1 in
this patch series removed), so this patch shouldn't impact behavior at all.

Historical note: we briefly removed these APIs once before, in this commit:
https://hg.mozilla.org/mozilla-central/rev/c216ff19d690
...but we brought them back because we had a motivating use case at the time.
We don't have any such motivating use cases any more, though.  So, this patch
here is essentially a modernized version of that older commit.

Differential Revision: https://phabricator.services.mozilla.com/D108148

layout/base/PresShell.cpp

@@ -836,7 +836,6 @@ PresShell::PresShell(Document* aDocument)
       mFontSizeInflationForceEnabled(false),
       mFontSizeInflationDisabledInMasterProcess(false),
       mFontSizeInflationEnabled(false),
-      mPaintingIsFrozen(false),
       mIsNeverPainting(false),
       mResolutionUpdated(false),
       mResolutionUpdatedByApz(false),
@@ -905,13 +904,6 @@ PresShell::~PresShell() {
                    mLastCallbackEventRequest == nullptr,
                "post-reflow queues not empty.  This means we're leaking");
 
-  // Verify that if painting was frozen, but we're being removed from the tree,
-  // that we now re-enable painting on our refresh driver, since it may need to
-  // be re-used by another presentation.
-  if (mPaintingIsFrozen) {
-    mPresContext->RefreshDriver()->Thaw();
-  }
-
   MOZ_ASSERT(mAllocatedPointers.IsEmpty(),
              "Some pres arena objects were not freed");
 
@@ -11379,22 +11371,6 @@ bool PresShell::DetermineFontSizeInflationState() {
   return true;
 }
 
-void PresShell::PausePainting() {
-  if (GetPresContext()->RefreshDriver()->GetPresContext() != GetPresContext())
-    return;
-
-  mPaintingIsFrozen = true;
-  GetPresContext()->RefreshDriver()->Freeze();
-}
-
-void PresShell::ResumePainting() {
-  if (GetPresContext()->RefreshDriver()->GetPresContext() != GetPresContext())
-    return;
-
-  mPaintingIsFrozen = false;
-  GetPresContext()->RefreshDriver()->Thaw();
-}
-
 void PresShell::SyncWindowProperties(nsView* aView) {
   nsIFrame* frame = aView->GetFrame();
   if (frame && mPresContext) {