Add InterestsFetcher which retrieves a user's interests from the server.

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index 699002612e5efa11bfa7d235fa6e47393688dcc3..036888949a3a385d0a7fe5b6f5b5d9b1c3b7ba66 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -687,6 +687,9 @@ const char kInstallSupervisedUserWhitelists[] =
 // Marks a renderer as an Instant process.
 const char kInstantProcess[]                = "instant-process";
 
+// The URL for the interests API.
+const char kInterestsURL[]                  = "interests-url";
+
 // Invalidation service should use GCM network channel even if experiment is not
 // enabled.
 const char kInvalidationUseGCMChannel[]     = "invalidation-use-gcm-channel";