Bug 1919611 - Fix #ifdef for windows. r=nchevobbe,dshin

And add a test.

Differential Revision: https://phabricator.services.mozilla.com/D222759

UltraBlame original commit: ab2530c2962f5b3e7e17dad49f6a6be59ee4b0b3

Author: marco-c

browser/components/tests/browser/browser.toml

@@ -30,6 +30,8 @@ reason = "test depends on update channel"
 ["browser_default_webprotocol_handler_mailto.js"]
 run-if = ["os == 'win'"]
 
+["browser_forced_colors.js"]
+
 ["browser_initial_tab_remoteType.js"]
 https_first_disabled = true
 

browser/components/tests/browser/browser_forced_colors.js

@@ -0,0 +1,20 @@
+
+
+
+"use strict";
+
+add_task(async function test_forced_colors_windows() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["ui.useAccessibilityTheme", 1]],
+  });
+
+  ok(
+    !matchMedia("(forced-colors: active)").matches,
+    "forced-colors: active shouldn't match in chrome"
+  );
+  is(
+    matchMedia("(forced-colors)").matches,
+    AppConstants.platform == "win",
+    "forced-colors should match with HCM enabled on windows, even in chrome"
+  );
+});

layout/base/nsPresContext.cpp

@@ -766,7 +766,7 @@ void nsPresContext::UpdateForcedColors(bool aNotify) {
 
 
 
-#ifdef XP_WINDOWS
+#ifdef XP_WIN
     if (prefs.mUseAccessibilityTheme && prefs.mIsChrome) {
       return StyleForcedColors::Requested;
     }