V8 Buildbot: Let leak checker use the v8-side wrapper.

scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux64___debug_builder.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "client.v8",
       "--builder",
       "V8 Linux64 - debug builder",
@@ skipping 273 matching lines @@
           "swarm_hashes": {
             "benchmarks": "[dummy hash for benchmarks]",
             "bot_default": "[dummy hash for bot_default]",
             "ignition": "[dummy hash for ignition]",
             "mjsunit": "[dummy hash for mjsunit]",
             "mozilla": "[dummy hash for mozilla]",
             "simdjs": "[dummy hash for simdjs]",
             "test262": "[dummy hash for test262]"
           }
         }
+      },
+      {
+        "builder_name": "V8 Linux64 - memcheck",
+        "properties": {
+          "parent_got_revision": "f2cbea7e89a45f46819777bb78a1f5bd0241f64c",
+          "parent_got_revision_cp": "refs/heads/master@{#50110}",
+          "parent_got_swarming_client_revision": "e4fee0b18f8163be6097c9c571640038896debc4",
+          "revision": "f2cbea7e89a45f46819777bb78a1f5bd0241f64c",
+          "swarm_hashes": {
+            "benchmarks": "[dummy hash for benchmarks]",
+            "bot_default": "[dummy hash for bot_default]",
+            "ignition": "[dummy hash for ignition]",
+            "mjsunit": "[dummy hash for mjsunit]",
+            "mozilla": "[dummy hash for mozilla]",
+            "simdjs": "[dummy hash for simdjs]",
+            "test262": "[dummy hash for test262]"
+          }
+        }
       }
     ],
     "~followup_annotations": [
-      "@@@STEP_TEXT@V8 Fuzzer<br />V8 Linux64 - debug<br />V8 Linux64 - debug - avx2<br />V8 Linux64 - debug - greedy allocator@@@"
+      "@@@STEP_TEXT@V8 Fuzzer<br />V8 Linux64 - debug<br />V8 Linux64 - debug - avx2<br />V8 Linux64 - debug - greedy allocator<br />V8 Linux64 - memcheck@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]