Bug 1249389 - part 6 - provide UniquePtr overload for nsIStartupCache::GetBuffer; r=erahm

The lone remaining startup cache-related uses of nsAutoArrayPtr are both
in TestStartupCache.cpp, for use with nsIStartupCache::GetBuffer.  The
uses can't use StartupCache::GetBuffer because StartupCache::GetBuffer
isn't visible outside of libxul, and TestStartupCache is a normal C++
unit test.

The Right Thing is to convert TestStartupCache to a gtest so we can see
libxul internal symbols and then delete nsIStartupCache entirely.
That's a bit complicated, as TestStartupCache doesn't fit nicely into
gtest's framework.  The simpler solution is to add a UniquePtr overload
in the interface that hides the XPCOM outparam management details.

startupcache/nsIStartupCache.idl

@@ -9,6 +9,10 @@
 #include "nsIObserver.idl"
 #include "nsIObjectOutputStream.idl"
 
+%{C++
+#include "mozilla/UniquePtr.h"
+%}
+
 [uuid(25957820-90a1-428c-8739-b0845d3cc534)]
 interface nsIStartupCache : nsISupports
 {
@@ -19,6 +23,18 @@ interface nsIStartupCache : nsISupports
    *  in that file. */
 
   uint32_t getBuffer(in string aID, out charPtr aBuffer);
+%{C++
+  /* A more convenient interface for using from C++.  */
+  nsresult GetBuffer(const char* id, mozilla::UniquePtr<char[]>* outbuf, uint32_t* length)
+  {
+    char* buf;
+    nsresult rv = GetBuffer(id, &buf, length);
+    NS_ENSURE_SUCCESS(rv, rv);
+    outbuf->reset(buf);
+    return rv;
+  }
+%}
+
   void putBuffer(in string aID, in string aBuffer, 
                             in uint32_t aLength);
  

startupcache/test/TestStartupCache.cpp

@@ -92,26 +92,23 @@ TestStartupWriteRead() {
   
   const char* buf = "Market opportunities for BeardBook";
   const char* id = "id";
-  char* outbufPtr = nullptr;
-  nsAutoArrayPtr<char> outbuf;  
+  UniquePtr<char[]> outbuf;  
   uint32_t len;
   
   rv = sc->PutBuffer(id, buf, strlen(buf) + 1);
   NS_ENSURE_SUCCESS(rv, rv);
   
-  rv = sc->GetBuffer(id, &outbufPtr, &len);
+  rv = sc->GetBuffer(id, &outbuf, &len);
   NS_ENSURE_SUCCESS(rv, rv);
-  outbuf = outbufPtr;
-  NS_ENSURE_STR_MATCH(buf, outbuf, "pre-write read");
+  NS_ENSURE_STR_MATCH(buf, outbuf.get(), "pre-write read");
 
   rv = sc->ResetStartupWriteTimer();
   rv = WaitForStartupTimer();
   NS_ENSURE_SUCCESS(rv, rv);
   
-  rv = sc->GetBuffer(id, &outbufPtr, &len);
+  rv = sc->GetBuffer(id, &outbuf, &len);
   NS_ENSURE_SUCCESS(rv, rv);
-  outbuf = outbufPtr;
-  NS_ENSURE_STR_MATCH(buf, outbuf, "simple write/read");
+  NS_ENSURE_STR_MATCH(buf, outbuf.get(), "simple write/read");
 
   return NS_OK;
 }