Bug 1876811: Remove nsPresContext's cache for about:config pref "layout.scrollbar.side". r=TYLin

Instead, just directly use the StaticPrefs getter for this pref at the one
usage-site, and remove the now-unnecessary GetCachedIntPref getter and
enum-parameter-type that was previously used to query the value.

This patch doesn't change behavior.

Differential Revision: https://phabricator.services.mozilla.com/D199782

layout/base/nsPresContext.cpp

@@ -274,7 +274,6 @@ nsPresContext::nsPresContext(dom::Document* aDocument, nsPresContextType aType)
       mCanPaginatedScroll(false),
       mDoScaledTwips(true),
       mIsRootPaginatedDocument(false),
-      mPrefScrollbarSide(0),
       mPendingThemeChanged(false),
       mPendingThemeChangeKind(0),
       mPendingUIResolutionChanged(false),
@@ -432,8 +431,6 @@ void nsPresContext::GetUserPreferences() {
 
   PreferenceSheet::EnsureInitialized();
 
-  mPrefScrollbarSide = StaticPrefs::layout_scrollbar_side();
-
   Document()->SetMayNeedFontPrefsUpdate();
 
   // * image animation

layout/base/nsPresContext.h

@@ -101,9 +101,6 @@ class PaletteCache;
 }  // namespace gfx
 }  // namespace mozilla
 
-// supported values for cached integer pref types
-enum nsPresContext_CachedIntPrefType { kPresContext_ScrollbarSide = 1 };
-
 // IDs for the default variable and fixed fonts (not to be changed, see
 // nsFont.h) To be used for Get/SetDefaultFont(). The other IDs in nsFont.h are
 // also supported.
@@ -376,21 +373,6 @@ class nsPresContext : public nsISupports, public mozilla::SupportsWeakPtr {
    */
   void EmulateMedium(nsAtom* aMediaType);
 
-  /** Get a cached integer pref, by its type */
-  // *  - initially created for bugs 30910, 61883, 74186, 84398
-  int32_t GetCachedIntPref(nsPresContext_CachedIntPrefType aPrefType) const {
-    // If called with a constant parameter, the compiler should optimize
-    // this switch statement away.
-    switch (aPrefType) {
-      case kPresContext_ScrollbarSide:
-        return mPrefScrollbarSide;
-      default:
-        NS_ERROR("invalid arg passed to GetCachedIntPref");
-    }
-
-    return false;
-  }
-
   const mozilla::PreferenceSheet::Prefs& PrefSheetPrefs() const {
     return mozilla::PreferenceSheet::PrefsFor(*mDocument);
   }
@@ -1352,7 +1334,6 @@ class nsPresContext : public nsISupports, public mozilla::SupportsWeakPtr {
   unsigned mCanPaginatedScroll : 1;
   unsigned mDoScaledTwips : 1;
   unsigned mIsRootPaginatedDocument : 1;
-  unsigned mPrefScrollbarSide : 2;
   unsigned mPendingThemeChanged : 1;
   // widget::ThemeChangeKind
   unsigned mPendingThemeChangeKind : kThemeChangeKindBits;

layout/generic/nsGfxScrollFrame.cpp

@@ -6018,15 +6018,13 @@ nsSize nsHTMLScrollFrame::GetSnapportSize() const {
 }
 
 bool nsHTMLScrollFrame::IsScrollbarOnRight() const {
-  nsPresContext* presContext = PresContext();
-
   // The position of the scrollbar in top-level windows depends on the pref
   // layout.scrollbar.side. For non-top-level elements, it depends only on the
   // directionaliy of the element (equivalent to a value of "1" for the pref).
   if (!mIsRoot) {
     return IsPhysicalLTR();
   }
-  switch (presContext->GetCachedIntPref(kPresContext_ScrollbarSide)) {
+  switch (StaticPrefs::layout_scrollbar_side()) {
     default:
     case 0:  // UI directionality
       return StaticPrefs::bidi_direction() == IBMBIDI_TEXTDIRECTION_LTR;