Issue #2858 - keep type in line with definition.

Depending on target platform, `AddRef()` returns either `unsigned long` or
`uint32_t`. Make the resulting type match for better optimization.

caps/nsPrincipal.cpp

@@ -471,7 +471,7 @@ nsPrincipal::Write(nsIObjectOutputStream* aStream)
   // TODO: figure out exactly why this happens and fix the root cause.
   nsCSPContext* CSPContext = static_cast<nsCSPContext*>(mCSP.get());
   if(CSPContext) {
-    int8_t CSPDepth = CSPContext->AddRef();
+    auto CSPDepth = CSPContext->AddRef();
     CSPContext->Release();
     if(CSPDepth > 2) return NS_OK;
   }