Bug 1743339 - Make NativeKeyBindings for single line editor try the one for multiline editor too r=stransky

`GtkEntry` is used to check what editing or natvigation command is
mapped to every key combination when `<input>` has focus.  However,
it does not support `select-all` signal, thus, Gecko does not respect
native shortcut key for "Select All".

This patch makes it try to check whether the given key combination is
mapped to "Select All" or not in `GtkTextView` widget which supports
`select-all` signal.  Thus, we'll get consistent behavior between
`<input>` and `<textarea>` about "Select All".

Differential Revision: https://phabricator.services.mozilla.com/D132450

modules/libpref/init/StaticPrefList.yaml

@@ -11582,6 +11582,19 @@
 #endif
   mirror: always
 
+#ifdef MOZ_WIDGET_GTK
+# Only GtkTextView (native multiline text viewer/editor) supports "select-all"
+# signal so that we cannot know "select-all" key bindings only with GtkEntry.
+# When this pref is set to true, if a key combination does not cause any
+# signals in GtkEntry, try to check the key combination is mapped to
+# "select-all" in GtkTextView or not.  If it's mapped to other commands, they
+# are just ignored.
+- name: ui.key.use_select_all_in_single_line_editor
+  type: bool
+  value: @IS_NIGHTLY_BUILD@
+  mirror: always
+#endif
+
 # Duration of timeout of incremental search in menus (ms).  0 means infinite.
 - name: ui.menu.incremental_search.timeout
   type: uint32_t

widget/gtk/NativeKeyBindings.cpp

@@ -6,6 +6,7 @@
 #include "mozilla/ArrayUtils.h"
 #include "mozilla/MathAlgorithms.h"
 #include "mozilla/Maybe.h"
+#include "mozilla/StaticPrefs_ui.h"
 #include "mozilla/TextEvents.h"
 #include "mozilla/WritingModes.h"
 
@@ -334,6 +335,23 @@ void NativeKeyBindings::GetEditCommands(const WidgetKeyboardEvent& aEvent,
     }
   }
 
+  // If the key event does not cause any commands, and we're for single line
+  // editor, let's check whether the key combination is for "select-all" in
+  // GtkTextView because the signal is not supported by GtkEntry.
+  if (aCommands.IsEmpty() && this == sInstanceForSingleLineEditor &&
+      StaticPrefs::ui_key_use_select_all_in_single_line_editor()) {
+    if (NativeKeyBindings* bindingsForMultilineEditor =
+            GetInstance(nsIWidget::NativeKeyBindingsForMultiLineEditor)) {
+      bindingsForMultilineEditor->GetEditCommands(aEvent, aWritingMode,
+                                                  aCommands);
+      if (aCommands.Length() == 1u &&
+          aCommands[0u] == static_cast<CommandInt>(Command::SelectAll)) {
+        return;
+      }
+      aCommands.Clear();
+    }
+  }
+
   /*
   gtk_bindings_activate_event is preferable, but it has unresolved bug:
   http://bugzilla.gnome.org/show_bug.cgi?id=162726