Switch base::Value typemapping to be by value instead of by unique_ptr.

extensions/browser/sandboxed_unpacker.cc

Index: extensions/browser/sandboxed_unpacker.cc
diff --git a/extensions/browser/sandboxed_unpacker.cc b/extensions/browser/sandboxed_unpacker.cc
index 730ac6b1d018f55ad7c3c14ddb7da59d72499427..44d19a5fdba117f044140e793a97e30bd5e96f38 100644
--- a/extensions/browser/sandboxed_unpacker.cc
+++ b/extensions/browser/sandboxed_unpacker.cc
@@ -426,7 +426,7 @@ void SandboxedUnpacker::Unpack(const base::FilePath& directory) {
 
 void SandboxedUnpacker::UnpackDone(
     const base::string16& error,
-    std::unique_ptr<base::DictionaryValue> manifest) {
+    const base::Optional<base::DictionaryValue>& manifest) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
 
   utility_process_mojo_client_.reset();
@@ -440,7 +440,7 @@ void SandboxedUnpacker::UnpackDone(
 
   unpacker_io_task_runner_->PostTask(
       FROM_HERE, base::Bind(&SandboxedUnpacker::UnpackExtensionSucceeded, this,
-                            base::Passed(&manifest)));
+                            base::Passed(manifest->CreateDeepCopy())));
 }
 
 void SandboxedUnpacker::UnpackExtensionSucceeded(