[ios] Adds a VoiceSearchController interface to the provider layer.

ios/chrome/browser/voice/BUILD.gn

Index: ios/chrome/browser/voice/BUILD.gn
diff --git a/ios/chrome/browser/voice/BUILD.gn b/ios/chrome/browser/voice/BUILD.gn
index 9319d04b3baf20779f0c39a061a31c07d9d60691..1ac78f87c5f5bafde597d2301aafd20825c8b58f 100644
--- a/ios/chrome/browser/voice/BUILD.gn
+++ b/ios/chrome/browser/voice/BUILD.gn
@@ -13,6 +13,11 @@ source_set("voice") {
     "speech_input_locale_match_config.mm",
   ]
 
+  deps = [
+    "//components/pref_registry",
+    "//components/prefs",
+  ]
+
   public_deps = [
     "//base",
     "//ios/chrome/browser",
@@ -20,6 +25,19 @@ source_set("voice") {
   ]
 }
 
+source_set("prefs") {
+  sources = [
+    "voice_search_prefs_registration.cc",
+    "voice_search_prefs_registration.h",
+  ]
+
+  deps = [
+    "//components/pref_registry",
+    "//components/prefs",
+    "//ios/public/provider/chrome/browser",
+  ]
+}
+
 source_set("tts") {
   sources = [
     "text_to_speech_listener.h",