Revert of Enable Site Isolation for Extensions.

chrome/common/extensions/extension_process_policy.cc

Index: chrome/common/extensions/extension_process_policy.cc
diff --git a/chrome/common/extensions/extension_process_policy.cc b/chrome/common/extensions/extension_process_policy.cc
index 914427763bfd510328b9217a8b9d0df3e4cdd7e8..3208e21d800491a6e3254932c3bef4c765f5bbdd 100644
--- a/chrome/common/extensions/extension_process_policy.cc
+++ b/chrome/common/extensions/extension_process_policy.cc
@@ -68,7 +68,16 @@
 }
 
 bool IsIsolateExtensionsEnabled() {
-  return true;
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kIsolateExtensions)) {
+    return true;
+  }
+
+  const std::string group_name =
+      base::FieldTrialList::FindFullName("SiteIsolationExtensions");
+  // Use StartsWith() for more flexibility (e.g. multiple Enabled groups).
+  return base::StartsWith(group_name, "Enabled",
+                          base::CompareCase::INSENSITIVE_ASCII);
 }
 
 }  // namespace extensions