Bug 1796044 - part 14: Get rid of `intl.tsf.associate_imc_only_when_imm_ime_is_active` r=m_kato

It's introduced in bug 1367692 to make it possible to test the bug of old
MS-IME on Windows 10 with later versions.  Now, the bug and the old versions
have gone.  Therefore, we don't need this pref anymore.

Depends on D159816

Differential Revision: https://phabricator.services.mozilla.com/D159817

modules/libpref/init/all.js

@@ -2544,12 +2544,6 @@ pref("font.size.monospace.x-math", 13);
   // Support IMEs implemented with IMM in TSF mode.
   pref("intl.tsf.support_imm", true);
 
-  // This is referred only when both "intl.tsf.enable" and
-  // "intl.tsf.support_imm" are true.  When this is true, default IMC is
-  // associated with focused window only when active keyboard layout is a
-  // legacy IMM-IME.
-  pref("intl.tsf.associate_imc_only_when_imm_ime_is_active", false);
-
   // If composition_font is set, Gecko sets the font to IME.  IME may use
   // the fonts on their window like candidate window.  If they are empty,
   // Gecko uses the system default font which is set to the IM context.

widget/windows/WinIMEHandler.cpp

@@ -7,7 +7,7 @@
 
 #include "IMMHandler.h"
 #include "mozilla/Preferences.h"
-#include "mozilla/StaticPrefList_intl.h"
+#include "mozilla/StaticPrefs_intl.h"
 #include "mozilla/TextEvents.h"
 #include "mozilla/WindowsVersion.h"
 #include "nsWindowDefs.h"
@@ -59,7 +59,6 @@ bool IMEHandler::sHasNativeCaretBeenRequested = false;
 
 bool IMEHandler::sIsInTSFMode = false;
 bool IMEHandler::sIsIMMEnabled = true;
-bool IMEHandler::sAssociateIMCOnlyWhenIMM_IMEActive = false;
 decltype(SetInputScopes)* IMEHandler::sSetInputScopes = nullptr;
 
 static POWER_PLATFORM_ROLE sPowerPlatformRole = PlatformRoleUnspecified;
@@ -71,10 +70,6 @@ void IMEHandler::Initialize() {
   sIsInTSFMode = TSFTextStore::IsInTSFMode();
   sIsIMMEnabled =
       !sIsInTSFMode || Preferences::GetBool("intl.tsf.support_imm", true);
-  sAssociateIMCOnlyWhenIMM_IMEActive =
-      sIsIMMEnabled &&
-      Preferences::GetBool("intl.tsf.associate_imc_only_when_imm_ime_is_active",
-                           false);
   if (!sIsInTSFMode) {
     // When full TSFTextStore is not available, try to use SetInputScopes API
     // to enable at least InputScope. Use GET_MODULE_HANDLE_EX_FLAG_PIN to
@@ -414,10 +409,7 @@ void IMEHandler::OnDestroyWindow(nsWindow* aWindow) {
 }
 
 // static
-bool IMEHandler::NeedsToAssociateIMC() {
-  return !sForceDisableCurrentIMM_IME &&
-         (!sAssociateIMCOnlyWhenIMM_IMEActive || !IsIMMActive());
-}
+bool IMEHandler::NeedsToAssociateIMC() { return !sForceDisableCurrentIMM_IME; }
 
 // static
 void IMEHandler::SetInputContext(nsWindow* aWindow, InputContext& aInputContext,
@@ -542,31 +534,6 @@ void IMEHandler::OnKeyboardLayoutChanged() {
   if (!sIsIMMEnabled || !IsTSFAvailable()) {
     return;
   }
-
-  // We don't need to do anything when sAssociateIMCOnlyWhenIMM_IMEActive is
-  // false because IMContext won't be associated/disassociated when changing
-  // active keyboard layout/IME.
-  if (!sAssociateIMCOnlyWhenIMM_IMEActive) {
-    return;
-  }
-
-  // If there is no TSFTextStore which has focus, i.e., no editor has focus,
-  // nothing to do here.
-  nsWindow* windowBase = TSFTextStore::GetEnabledWindowBase();
-  if (!windowBase) {
-    return;
-  }
-
-  // If IME isn't available, nothing to do here.
-  InputContext inputContext = windowBase->GetInputContext();
-  if (!WinUtils::IsIMEEnabled(inputContext)) {
-    return;
-  }
-
-  // Associate or Disassociate IMC if it's necessary.
-  // Note that this does nothing if the window has already associated with or
-  // disassociated from the window.
-  AssociateIMEContext(windowBase, NeedsToAssociateIMC());
 }
 
 // static

widget/windows/WinIMEHandler.h

@@ -202,7 +202,6 @@ class IMEHandler final {
   // If sIMMEnabled is false, any IME messages are not handled in TSF mode.
   // Additionally, IME context is always disassociated from focused window.
   static bool sIsIMMEnabled;
-  static bool sAssociateIMCOnlyWhenIMM_IMEActive;
 
   static bool IsTSFAvailable() { return sIsInTSFMode; }
   static bool IsIMMActive();