Get rid of MessageLoop* caching in extensions code.

chrome/browser/extensions/sandboxed_extension_unpacker.cc

Index: chrome/browser/extensions/sandboxed_extension_unpacker.cc
===================================================================
--- chrome/browser/extensions/sandboxed_extension_unpacker.cc	(revision 30521)
+++ chrome/browser/extensions/sandboxed_extension_unpacker.cc	(working copy)
@@ -29,14 +29,14 @@
 SandboxedExtensionUnpacker::SandboxedExtensionUnpacker(
     const FilePath& crx_path, ResourceDispatcherHost* rdh,
     SandboxedExtensionUnpackerClient* client)
-      : crx_path_(crx_path), file_loop_(NULL), rdh_(rdh), client_(client),
-        got_response_(false) {
+      : crx_path_(crx_path), thread_identifier_(ChromeThread::ID_COUNT),
+        rdh_(rdh), client_(client), got_response_(false) {
 }
 
 void SandboxedExtensionUnpacker::Start() {
   // We assume that we are started on the thread that the client wants us to do
   // file IO on.
-  file_loop_ = MessageLoop::current();
+  CHECK(ChromeThread::GetCurrentThreadIdentifier(&thread_identifier_));
 
   // Create a temporary directory to work in.
   if (!temp_dir_.CreateUniqueTempDir()) {
@@ -91,13 +91,14 @@
 
 void SandboxedExtensionUnpacker::StartProcessOnIOThread(
     const FilePath& temp_crx_path) {
-  UtilityProcessHost* host = new UtilityProcessHost(rdh_, this, file_loop_);
+  UtilityProcessHost* host = new UtilityProcessHost(
+      rdh_, this, thread_identifier_);
   host->StartExtensionUnpacker(temp_crx_path);
 }
 
 void SandboxedExtensionUnpacker::OnUnpackExtensionSucceeded(
     const DictionaryValue& manifest) {
-  DCHECK(file_loop_ == MessageLoop::current());
+  DCHECK(ChromeThread::CurrentlyOn(thread_identifier_));
   got_response_ = true;
 
   ExtensionUnpacker::DecodedImages images;
@@ -198,7 +199,7 @@
 
 void SandboxedExtensionUnpacker::OnUnpackExtensionFailed(
     const std::string& error) {
-  DCHECK(file_loop_ == MessageLoop::current());
+  DCHECK(ChromeThread::CurrentlyOn(thread_identifier_));
   got_response_ = true;
   ReportFailure(error);
 }