Prevent extension sideloading from Windows registry

extensions/common/extension.h

Index: extensions/common/extension.h
diff --git a/extensions/common/extension.h b/extensions/common/extension.h
index 47f85f33ff942bd704b47558d45061217ebb2148..de0e2f584c508b04a477e11eb4236ff10cd45a73 100644
--- a/extensions/common/extension.h
+++ b/extensions/common/extension.h
@@ -166,6 +166,12 @@ class Extension : public base::RefCountedThreadSafe<Extension> {
     // custodian of a supervised user.
     WAS_INSTALLED_BY_CUSTODIAN = 1 << 11,
 
+    // |MAY_BE_UNTRUSTED| indicates that this extension came from a potentially
+    // unsafe source (e.g., sideloaded from a local CRX file via the Windows
+    // registry). Such extensions may be subjected to additional constraints
+    // before they are fully installed and enabled.
+    MAY_BE_UNTRUSTED = 1 << 12,
+
     // When adding new flags, make sure to update kInitFromValueFlagBits.
   };