Bug 1311933 - P1. Use integer as the key of safebrowsing cache. r=francois

In Bug 1323953, we always send 4-bytes prefix for completion and the prefix is also
used as the key to store cache result from gethash request.
Since it is always 4-bytes, we could convert it to integer for simplicity.

MozReview-Commit-ID: Lkvrg0wvX5Z

toolkit/components/url-classifier/HashStore.cpp

@@ -194,11 +194,11 @@ TableUpdateV4::NewChecksum(const std::string& aChecksum)
 }
 
 nsresult
-TableUpdateV4::NewFullHashResponse(const nsACString& aPrefix,
+TableUpdateV4::NewFullHashResponse(const Prefix& aPrefix,
                                    CachedFullHashResponse& aResponse)
 {
   CachedFullHashResponse* response =
-    mFullHashResponseMap.LookupOrAdd(aPrefix);
+    mFullHashResponseMap.LookupOrAdd(aPrefix.ToUint32());
   if (!response) {
     return NS_ERROR_OUT_OF_MEMORY;
   }