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

docshell/base/nsIContentViewer.idl

@@ -288,18 +288,6 @@ interface nsIContentViewer : nsISupports
   void getContentSizeConstrained(in long maxWidth, in long maxHeight,
                                  out long width, out long height);
 
-  /**
-   * Instruct the refresh driver to discontinue painting until further
-   * notice.
-   */
-  void pausePainting();
-
-  /**
-   * Instruct the refresh driver to resume painting after a previous call to
-   * pausePainting().
-   */
-  void resumePainting();
-
   [noscript, notxpcom] Encoding getHintCharset();
   [noscript, notxpcom] void setHintCharset(in Encoding aEncoding);
 };

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) {

layout/base/PresShell.h

@@ -681,20 +681,6 @@ class PresShell final : public nsStubDocumentObserver,
    */
   bool IsPaintingSuppressed() const { return mPaintingSuppressed; }
 
-  /**
-   * Pause painting by freezing the refresh driver of this and all parent
-   * presentations. This may not have the desired effect if this pres shell
-   * has its own refresh driver.
-   */
-  void PausePainting();
-
-  /**
-   * Resume painting by thawing the refresh driver of this and all parent
-   * presentations. This may not have the desired effect if this pres shell
-   * has its own refresh driver.
-   */
-  void ResumePainting();
-
   /**
    * Unsuppress painting.
    */
@@ -3080,8 +3066,6 @@ class PresShell final : public nsStubDocumentObserver,
   bool mFontSizeInflationDisabledInMasterProcess : 1;
   bool mFontSizeInflationEnabled : 1;
 
-  bool mPaintingIsFrozen : 1;
-
   // If a document belongs to an invisible DocShell, this flag must be set
   // to true, so we can avoid any paint calls for widget related to this
   // presshell.

layout/base/nsDocumentViewer.cpp

@@ -2690,28 +2690,6 @@ nsDocumentViewer::SetHintCharset(const Encoding* aEncoding) {
   CallChildren(childFn);
 }
 
-NS_IMETHODIMP
-nsDocumentViewer::PausePainting() {
-  CallChildren([](nsDocumentViewer* aChild) { aChild->PausePainting(); });
-
-  if (PresShell* presShell = GetPresShell()) {
-    presShell->PausePainting();
-  }
-
-  return NS_OK;
-}
-
-NS_IMETHODIMP
-nsDocumentViewer::ResumePainting() {
-  CallChildren([](nsDocumentViewer* aChild) { aChild->ResumePainting(); });
-
-  if (PresShell* presShell = GetPresShell()) {
-    presShell->ResumePainting();
-  }
-
-  return NS_OK;
-}
-
 nsresult nsDocumentViewer::GetContentSizeInternal(int32_t* aWidth,
                                                   int32_t* aHeight,
                                                   nscoord aMaxWidth,