Bug 1908664 - Add nsIPrincipal::GetIsInPrivateBrowsing r=media-playback-reviewers,anti-tracking-reviewers,dom-storage-reviewers,padenot,asuth,pbz

Differential Revision: https://phabricator.services.mozilla.com/D216993

caps/BasePrincipal.cpp

@@ -1183,6 +1183,12 @@ BasePrincipal::GetPrivateBrowsingId(uint32_t* aPrivateBrowsingId) {
   return NS_OK;
 }
 
+NS_IMETHODIMP
+BasePrincipal::GetIsInPrivateBrowsing(bool* aIsInPrivateBrowsing) {
+  *aIsInPrivateBrowsing = mOriginAttributes.IsPrivateBrowsing();
+  return NS_OK;
+}
+
 nsresult BasePrincipal::GetAddonPolicy(
     extensions::WebExtensionPolicy** aResult) {
   AssertIsOnMainThread();

caps/BasePrincipal.h

@@ -165,6 +165,7 @@ class BasePrincipal : public nsJSPrincipals {
   NS_IMETHOD GetIsOnion(bool* aIsOnion) override;
   NS_IMETHOD GetUserContextId(uint32_t* aUserContextId) final;
   NS_IMETHOD GetPrivateBrowsingId(uint32_t* aPrivateBrowsingId) final;
+  NS_IMETHOD GetIsInPrivateBrowsing(bool* aIsInPrivateBrowsing) final;
   NS_IMETHOD GetSiteOrigin(nsACString& aSiteOrigin) final;
   NS_IMETHOD GetSiteOriginNoSuffix(nsACString& aSiteOrigin) override;
   NS_IMETHOD IsThirdPartyURI(nsIURI* uri, bool* aRes) override;

caps/nsIPrincipal.idl

@@ -587,6 +587,14 @@ interface nsIPrincipal : nsISupports
      */
     [infallible] readonly attribute unsigned long privateBrowsingId;
 
+    /**
+     * Retuns true if it is in private browsing based on privateBrowsingId
+     * being non-zero.
+     *
+     * May be called from any thread.
+     */
+    [infallible] readonly attribute boolean isInPrivateBrowsing;
+
     /**
      * Returns true iff this is a null principal (corresponding to an
      * unknown, hence assumed minimally privileged, security context).