Bug 1573992 - Convert ui.scrolling.negate_wheel_scroll to static pref. r=njn

Converts ui.scrolling.negate_wheel_scroll to a static pref and updates its usages. This one is only enabled on android, so I used the IS_ANDROID value to fill it.

Differential Revision: https://phabricator.services.mozilla.com/D42394

--HG--
extra : moz-landing-system : lando

mobile/android/app/mobile.js

@@ -613,8 +613,6 @@ pref("ui.scrolling.overscroll_snap_limit", -1);
 pref("ui.scrolling.min_scrollable_distance", -1);
 // The axis lock mode for panning behaviour - set between standard, free and sticky
 pref("ui.scrolling.axis_lock_mode", "standard");
-// Negate scroll, true will make the mouse scroll wheel move the screen the same direction as with most desktops or laptops.
-pref("ui.scrolling.negate_wheel_scroll", true);
 // Determine the dead zone for gamepad joysticks. Higher values result in larger dead zones; use a negative value to
 // auto-detect based on reported hardware values
 pref("ui.scrolling.gamepad_dead_zone", 115);

modules/libpref/init/StaticPrefList.yaml

@@ -6718,6 +6718,13 @@
 #endif
   mirror: always
 
+# Negate scroll, true will make the mouse scroll wheel move the screen the
+# same direction as with most desktops or laptops.
+- name: ui.scrolling.negate_wheel_scroll
+  type: bool
+  value: @IS_ANDROID@
+  mirror: always
+
 # If the user puts a finger down on an element and we think the user might be
 # executing a pan gesture, how long do we wait before tentatively deciding the
 # gesture is actually a tap and activating the target element?

widget/android/nsWindow.cpp

@@ -15,6 +15,7 @@
 #include "mozilla/MouseEvents.h"
 #include "mozilla/Preferences.h"
 #include "mozilla/RWLock.h"
+#include "mozilla/StaticPrefs_ui.h"
 #include "mozilla/TouchEvents.h"
 #include "mozilla/TypeTraits.h"
 #include "mozilla/Unused.h"
@@ -363,8 +364,6 @@ class nsWindow::NPZCSupport final
     : public PanZoomController::NativeProvider::Natives<NPZCSupport> {
   using LockedWindowPtr = WindowPtr<NPZCSupport>::Locked;
 
-  static bool sNegateWheelScroll;
-
   WindowPtr<NPZCSupport> mWindow;
   PanZoomController::NativeProvider::WeakRef mNPZC;
   int mPreviousButtons;
@@ -413,13 +412,6 @@ class nsWindow::NPZCSupport final
               const PanZoomController::NativeProvider::LocalRef& aNPZC)
       : mWindow(aPtr, aWindow), mNPZC(aNPZC), mPreviousButtons(0) {
     MOZ_ASSERT(mWindow);
-
-    static bool sInited;
-    if (!sInited) {
-      Preferences::AddBoolVarCache(&sNegateWheelScroll,
-                                   "ui.scrolling.negate_wheel_scroll");
-      sInited = true;
-    }
   }
 
   ~NPZCSupport() {}
@@ -508,7 +500,7 @@ class nsWindow::NPZCSupport final
 
     ScreenPoint origin = ScreenPoint(aX, aY);
 
-    if (sNegateWheelScroll) {
+    if (StaticPrefs::ui_scrolling_negate_wheel_scroll()) {
       aHScroll = -aHScroll;
       aVScroll = -aVScroll;
     }
@@ -779,8 +771,6 @@ class nsWindow::NPZCSupport final
 template <>
 const char nsWindow::NativePtr<nsWindow::NPZCSupport>::sName[] = "NPZCSupport";
 
-bool nsWindow::NPZCSupport::sNegateWheelScroll;
-
 NS_IMPL_ISUPPORTS(nsWindow::AndroidView, nsIAndroidEventDispatcher,
                   nsIAndroidView)