[Fallback Icons] Refactor FallbackIconService to be a BrowserContext-level singleton

chrome/test/base/testing_profile.h

Index: chrome/test/base/testing_profile.h
diff --git a/chrome/test/base/testing_profile.h b/chrome/test/base/testing_profile.h
index 8db54eea1cb6ddf1d9fd6b1ddd14430a5ceee98e..1cf11c4c982c1640490add1fedf09e8695c7da29 100644
--- a/chrome/test/base/testing_profile.h
+++ b/chrome/test/base/testing_profile.h
@@ -6,6 +6,8 @@
 #define CHROME_TEST_BASE_TESTING_PROFILE_H_
 
 #include <string>
+#include <utility>
+#include <vector>
 
 #include "base/files/scoped_temp_dir.h"
 #include "base/memory/ref_counted.h"
@@ -164,6 +166,9 @@ class TestingProfile : public Profile {
 
   ~TestingProfile() override;
 
+  // Creates the fallback icon service.
+  void CreateFallbackIconService();
+
   // Creates the favicon service. Consequent calls would recreate the service.
   void CreateFaviconService();