Side Search: remove enable_side_search build flag

Since side search is now supported on all desktop platforms,
enable_side_search build flag is not necessary any more.
Side search related code guarded by the old flag
should be under toolkit_view build flag after this CL.

Change-Id: Iff76b92a1150f0af0775268865d635bc9714952b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3614871
Reviewed-by: Peter Kasting <[email protected]>
Reviewed-by: Alexander Hendrich <[email protected]>
Reviewed-by: Scott Violet <[email protected]>
Reviewed-by: Gabriel Charette <[email protected]>
Commit-Queue: Yuheng Huang <[email protected]>
Reviewed-by: Thomas Lukaszewicz <[email protected]>
Reviewed-by: Charlie Harrison <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1000504}
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index dfff2d4..857a0588 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -459,6 +459,7 @@
 
 #if defined(TOOLKIT_VIEWS)
 #include "chrome/browser/ui/browser_view_prefs.h"
+#include "chrome/browser/ui/side_search/side_search_prefs.h"
 #endif
 
 #if BUILDFLAG(ENABLE_SESSION_SERVICE)
@@ -466,10 +467,6 @@
 #include "chrome/browser/sessions/session_service_log.h"
 #endif
 
-#if BUILDFLAG(ENABLE_SIDE_SEARCH)
-#include "chrome/browser/ui/side_search/side_search_prefs.h"
-#endif  // BUILDFLAG(ENABLE_SIDE_SEARCH)
-
 namespace {
 
 // Please keep the list of deprecated prefs in chronological order. i.e. Add to
@@ -1561,13 +1558,10 @@
 
 #if defined(TOOLKIT_VIEWS)
   accessibility_prefs::RegisterInvertBubbleUserPrefs(registry);
+  side_search_prefs::RegisterProfilePrefs(registry);
   RegisterBrowserViewProfilePrefs(registry);
 #endif
 
-#if BUILDFLAG(ENABLE_SIDE_SEARCH)
-  side_search_prefs::RegisterProfilePrefs(registry);
-#endif  // BUILDFLAG(ENABLE_SIDE_SEARCH)
-
 #if !BUILDFLAG(IS_ANDROID)
   registry->RegisterBooleanPref(
       prefs::kLensRegionSearchEnabled, true,