Bug 1517434 part 1. Add a fast inline nsIPrincipal::IsSystemPrincipal. r=mccr8

Differential Revision: https://phabricator.services.mozilla.com/D15672

--HG--
extra : moz-landing-system : lando

caps/BasePrincipal.cpp

@@ -266,7 +266,7 @@ BasePrincipal::GetIsExpandedPrincipal(bool* aResult) {
 
 NS_IMETHODIMP
 BasePrincipal::GetIsSystemPrincipal(bool* aResult) {
-  *aResult = Kind() == eSystemPrincipal;
+  *aResult = IsSystemPrincipal();
   return NS_OK;
 }
 

caps/BasePrincipal.h

@@ -134,6 +134,10 @@ class BasePrincipal : public nsJSPrincipals {
     return static_cast<BasePrincipal*>(aPrin);
   }
 
+  static const BasePrincipal* Cast(const nsIPrincipal* aPrin) {
+    return static_cast<const BasePrincipal*>(aPrin);
+  }
+
   static already_AddRefed<BasePrincipal> CreateCodebasePrincipal(
       const nsACString& aOrigin);
 
@@ -179,6 +183,9 @@ class BasePrincipal : public nsJSPrincipals {
   inline bool FastSubsumesIgnoringFPD(nsIPrincipal* aOther);
   inline bool FastSubsumesConsideringDomainIgnoringFPD(nsIPrincipal* aOther);
 
+  // Fast way to check whether we have a system principal.
+  inline bool IsSystemPrincipal() const;
+
   // Returns the principal to inherit when a caller with this principal loads
   // the given URI.
   //
@@ -342,6 +349,14 @@ inline bool BasePrincipal::FastSubsumesConsideringDomainIgnoringFPD(
   return FastSubsumesIgnoringFPD(aOther, ConsiderDocumentDomain);
 }
 
+inline bool BasePrincipal::IsSystemPrincipal() const {
+  return Kind() == eSystemPrincipal;
+}
+
 }  // namespace mozilla
 
+inline bool nsIPrincipal::IsSystemPrincipal() const {
+  return mozilla::BasePrincipal::Cast(this)->IsSystemPrincipal();
+}
+
 #endif /* mozilla_BasePrincipal_h */

caps/nsIPrincipal.idl

@@ -335,6 +335,14 @@ interface nsIPrincipal : nsISerializable
      */
     [infallible] readonly attribute boolean isSystemPrincipal;
 
+    /**
+     * Faster and nicer version callable from C++.  Callers must include
+     * BasePrincipal.h, where it's implemented.
+     */
+    %{C++
+      inline bool IsSystemPrincipal() const;
+    %}
+
     /**
      * Returns true iff the principal is either an addon principal or
      * an expanded principal, which contains at least one addon principal.