Speed up kTotalMorePrecise mode of Cord::EstimatedMemoryUsage() by about 25% by…

Speed up kTotalMorePrecise mode of Cord::EstimatedMemoryUsage() by about 25% by avoiding a redundant map lookup.

PiperOrigin-RevId: 556816759
Change-Id: I971e428bf12d91720df72a91cc0bdf0513b0c270

absl/strings/cord_analysis.cc

@@ -67,8 +67,7 @@ struct RawUsage<Mode::kTotalMorePrecise> {
   std::unordered_set<const CordRep*> counted;
 
   void Add(size_t size, CordRepRef<Mode::kTotalMorePrecise> repref) {
-    if (counted.find(repref.rep) == counted.end()) {
-      counted.insert(repref.rep);
+    if (counted.insert(repref.rep).second) {
       total += size;
     }
   }