Use local variable for out parameter rather than direct use of ivar

- Resolves spurious static analyzer warning about response_ being potentially leaked due to the retain in Xcode 6.3 and later.

I'm submitting this on behalf of Brian Moore.

R=qsr@chromium.org

Review URL: https://codereview.chromium.org/1171693007

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1460 4c0a9323-5329-0410-9bdc-e9ce6186880e

src/common/mac/HTTPMultipartUpload.m

@@ -195,10 +195,11 @@
   if ([[req URL] isFileURL]) {
     [[req HTTPBody] writeToURL:[req URL] options:0 error:error];
   } else {
+    NSURLResponse *response = nil;
     data = [NSURLConnection sendSynchronousRequest:req
-                                 returningResponse:&response_
+                                 returningResponse:&response
                                              error:error];
-    [response_ retain];
+    response_ = (NSHTTPURLResponse *)[response retain];
   }
   [req release];