Refactor ProtectedMediaIdentifierPermissionContext to derive from PermissionContextBase.

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 2dd3d98d05fd751176ab1467f50f5146d3a34688..675bc60c2868501f7815ec8085a6d30541771f11 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -52752,6 +52752,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="2" label="PERMISSION_PUSH_MESSAGING"/>
   <int value="3" label="PERMISSION_NOTIFICATIONS"/>
   <int value="4" label="PERMISSION_GEOLOCATION"/>
+  <int value="5" label="PERMISSION_PROTECTED_MEDIA"/>
 </enum>
 
 <enum name="PhotoEditorFileType" type="int">
@@ -60570,6 +60571,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <suffix name="PushMessaging" label="Push messaging permission actions"/>
   <suffix name="Notifications" label="Notification permission actions"/>
   <suffix name="Geolocation" label="Geolocation permission actions"/>
+  <suffix name="ProtectedMedia" label="Protected media permission actions"/>
   <affected-histogram name="ContentSettings.PermissionActions"/>
   <affected-histogram name="ContentSettings.PermissionActionsInsecureOrigin"/>
   <affected-histogram name="ContentSettings.PermissionActionsSecureOrigin"/>