Added "Enabled_V3" to PartitionAllocGigaCage.

Bug: 1086388
Change-Id: Ie0ddb53e5910fb4ee32592531fbb4ea5f4a794c5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2500972Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Takashi Sakamoto <tasak@google.com>
Cr-Commit-Position: refs/heads/master@{#821647}

testing/variations/fieldtrial_testing_config.json

@@ -5207,6 +5207,7 @@
                 "android",
                 "android_webview",
                 "chromeos",
+                "ios",
                 "linux",
                 "mac",
                 "windows"
@@ -5217,6 +5218,12 @@
                     "enable_features": [
                         "PartitionAllocGigaCage"
                     ]
+                },
+                {
+                    "name": "Enabled_V3",
+                    "enable_features": [
+                        "PartitionAllocGigaCage"
+                    ]
                 }
             ]
         }