Cleanup: Remove unneeded browser_thread.h includes.

chrome/browser/chromeos/extensions/external_cache.cc

Index: chrome/browser/chromeos/extensions/external_cache.cc
diff --git a/chrome/browser/chromeos/extensions/external_cache.cc b/chrome/browser/chromeos/extensions/external_cache.cc
index 6faa9b91e4748e20392b0242fec7eb8deabd9fd0..5b547a425f3729ff417c943c1876b7ab054c63a4 100644
--- a/chrome/browser/chromeos/extensions/external_cache.cc
+++ b/chrome/browser/chromeos/extensions/external_cache.cc
@@ -19,7 +19,6 @@
 #include "chrome/browser/extensions/external_provider_impl.h"
 #include "chrome/browser/extensions/updater/extension_downloader.h"
 #include "chrome/common/extensions/extension_constants.h"
-#include "content/public/browser/browser_thread.h"
 #include "content/public/browser/notification_details.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/notification_source.h"
@@ -92,7 +91,6 @@ void ExternalCache::OnDamagedFileDetected(const base::FilePath& path) {
     if (entry->GetString(extensions::ExternalProviderImpl::kExternalCrx,
                          &external_crx) &&
         external_crx == path.value()) {
-
       std::string id = it.key();
       LOG(ERROR) << "ExternalCache extension at " << path.value()
                  << " failed to install, deleting it.";