Move ExtensionDownloader to //extensions

This is a mechanical move with opportunistic clang_format
applied for cleanup.

This also introduces a dependency on //google_apis within
//extensions/browser.

BUG=398671

Review URL: https://codereview.chromium.org/654363002

Cr-Commit-Position: refs/heads/master@{#299957}
diff --git a/chrome/browser/extensions/extension_service.cc b/chrome/browser/extensions/extension_service.cc
index 56838a7..7afdf07b 100644
--- a/chrome/browser/extensions/extension_service.cc
+++ b/chrome/browser/extensions/extension_service.cc
@@ -42,7 +42,6 @@
 #include "chrome/browser/extensions/shared_module_service.h"
 #include "chrome/browser/extensions/unpacked_installer.h"
 #include "chrome/browser/extensions/updater/chrome_extension_downloader_factory.h"
-#include "chrome/browser/extensions/updater/extension_downloader.h"
 #include "chrome/browser/extensions/updater/extension_updater.h"
 #include "chrome/browser/google/google_brand.h"
 #include "chrome/browser/profiles/profile.h"
@@ -72,6 +71,7 @@
 #include "extensions/browser/uninstall_reason.h"
 #include "extensions/browser/update_observer.h"
 #include "extensions/browser/updater/extension_cache.h"
+#include "extensions/browser/updater/extension_downloader.h"
 #include "extensions/common/extension_messages.h"
 #include "extensions/common/extension_urls.h"
 #include "extensions/common/feature_switch.h"