Convert PermissionsBlacklist flag to base::Feature.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 2b27cb685bbb799ba897cf6f4ca8a0e6071ab96e..f783a3276d02e8df15ca614987c03ec4d4d34e61 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -91711,6 +91711,7 @@ value.
   <int value="636425179" label="mhtml-generator-option"/>
   <int value="637396292" label="AllBookmarks:enabled"/>
   <int value="643725031" label="disable-touch-feedback"/>
+  <int value="644189071" label="PermissionsBlacklist:enabled"/>
   <int value="646252875" label="ReadItLaterInMenu:enabled"/>
   <int value="646738320" label="disable-gesture-editing"/>
   <int value="650602639" label="enable-autofill-keyboard-accessory-view"/>
@@ -91725,6 +91726,7 @@ value.
   <int value="715617684" label="OriginTrials:disabled"/>
   <int value="716080990" label="restrict-iframe-permissions"/>
   <int value="730024226" label="enable-out-of-process-pdf"/>
+  <int value="730750097" label="PermissionsBlacklist:disabled"/>
   <int value="732703958" label="enable-gesture-tap-highlight"/>
   <int value="745868416" label="disable-system-timezone-automatic-detection"/>
   <int value="746944193" label="enable-automatic-password-saving:disabled"/>