Bug 1517385 - Add the pref to control the transition-duration. r=TYLin

Differential Revision: https://phabricator.services.mozilla.com/D96506

layout/base/AccessibleCaret.cpp

@@ -302,7 +302,10 @@ void AccessibleCaret::SetCaretElementStyle(const nsRect& aRect,
   styleStr.AppendLiteral("px; margin-left: ");
   styleStr.AppendFloat(StaticPrefs::layout_accessiblecaret_margin_left() /
                        aZoomLevel);
-  styleStr.AppendLiteral("px");
+  styleStr.AppendLiteral("px; transition-duration: ");
+  styleStr.AppendFloat(
+      StaticPrefs::layout_accessiblecaret_transition_duration());
+  styleStr.AppendLiteral("ms");
 
   CaretElement().SetAttr(kNameSpaceID_None, nsGkAtoms::style, styleStr, true);
   AC_LOG("%s: %s", __FUNCTION__, NS_ConvertUTF16toUTF8(styleStr).get());

layout/base/tests/marionette/test_accessiblecaret_cursor_mode.py

@@ -49,6 +49,9 @@ class AccessibleCaretCursorModeTestCase(MarionetteTestCase):
         self.prefs = {
             self.caret_tested_pref: True,
             self.hide_carets_for_mouse: False,
+            # To disable transition, or the caret may not be the desired
+            # location yet, we cannot press a caret successfully.
+            "layout.accessiblecaret.transition-duration": "0.0",
         }
         self.marionette.set_prefs(self.prefs)
         self.actions = CaretActions(self.marionette)

layout/base/tests/marionette/test_accessiblecaret_selection_mode.py

@@ -56,6 +56,9 @@ class AccessibleCaretSelectionModeTestCase(MarionetteTestCase):
         self.prefs = {
             "layout.word_select.eat_space_to_next_word": False,
             self.carets_tested_pref: True,
+            # To disable transition, or the caret may not be the desired
+            # location yet, we cannot press a caret successfully.
+            "layout.accessiblecaret.transition-duration": "0.0",
         }
         self.marionette.set_prefs(self.prefs)
         self.actions = CaretActions(self.marionette)

layout/style/res/ua.css

@@ -412,7 +412,6 @@ parsererror|sourcetext {
 
 div:-moz-native-anonymous.moz-accessiblecaret {
   /* Add transition effect to make caret size changing smoother. */
-  transition-duration: 250ms;
   transition-property: width, height, margin-left;
 
   position: absolute;

modules/libpref/init/StaticPrefList.yaml

@@ -5823,6 +5823,11 @@
   value: -18.5f
   mirror: always
 
+- name: layout.accessiblecaret.transition-duration
+  type: float
+  value: 250.0f
+  mirror: always
+
 # Simulate long tap events to select words. Mainly used in manual testing
 # with mouse.
 - name: layout.accessiblecaret.use_long_tap_injector