Distrust the remainder of the Symantec Legacy PKI

As previously communicated, and as documented at at
https://g.co/chrome/symantecpkicerts, certificates issued
by the Symantec Legacy PKI Infrastructure between
2016-06-01 and 2017-12-01 will no longer be trusted. This
changes the default state to remove trust in these
certificates. Certificates issued under the DigiCert
Managed PKI, or those from previously-identified,
independent third-party CAs, are not affected.

Bug: 796230, 805460
Change-Id: I74bdecc9dfdd66dec1a111f9eddb830babfa8222
Reviewed-on: https://chromium-review.googlesource.com/1134209
Commit-Queue: Nick Harper <nharper@chromium.org>
Reviewed-by: Nick Harper <nharper@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577764}

net/cert/cert_verify_proc.cc

@@ -912,6 +912,6 @@ const base::Feature CertVerifyProc::kSHA1LegacyMode{
 
 // static
 const base::Feature CertVerifyProc::kLegacySymantecPKIEnforcement{
-    "LegacySymantecPKI", base::FEATURE_DISABLED_BY_DEFAULT};
+    "LegacySymantecPKI", base::FEATURE_ENABLED_BY_DEFAULT};
 
 }  // namespace net