Merge pull request #23836 from vjpai/expect_me_maybe

Make MaybeExpect guarantee at-most-once and allow Verify reuse

test/cpp/end2end/async_end2end_test.cc

@@ -120,6 +120,7 @@ class Verifier {
     while (!expectations_.empty()) {
       Next(cq, ignore_ok);
     }
+    maybe_expectations_.clear();
   }
 
   // This version of Verify stops after a certain deadline
@@ -139,6 +140,7 @@ class Verifier {
         GotTag(got_tag, ok, false);
       }
     }
+    maybe_expectations_.clear();
   }
 
   // This version of Verify stops after a certain deadline, and uses the
@@ -161,6 +163,7 @@ class Verifier {
         GotTag(got_tag, ok, false);
       }
     }
+    maybe_expectations_.clear();
   }
 
  private:
@@ -181,6 +184,7 @@ class Verifier {
         if (!ignore_ok) {
           EXPECT_EQ(it2->second.ok, ok);
         }
+        maybe_expectations_.erase(it2);
       } else {
         gpr_log(GPR_ERROR, "Unexpected tag: %p", got_tag);
         abort();