AU: Full proxy support

This CL Introduces a new proxy resolver that queries Chrome browser
for all URLs. This means the updater now works with Proxy
AutoConfiguration (PAC) files and automatic proxy detection.

BUG=chromium-os:9478
TEST=performed update, unittests

Review URL: http://codereview.chromium.org/6594025

Change-Id: I2c169aec06109e3eabc4011e0b536685dfd13f79
diff --git a/update_attempter.cc b/update_attempter.cc
index 949434e..e49a551 100644
--- a/update_attempter.cc
+++ b/update_attempter.cc
@@ -125,6 +125,7 @@
 void UpdateAttempter::Update(const std::string& app_version,
                              const std::string& omaha_url,
                              bool obey_proxies) {
+  chrome_proxy_resolver_.Init();
   if (status_ == UPDATE_STATUS_UPDATED_NEED_REBOOT) {
     LOG(INFO) << "Not updating b/c we already updated and we're waiting for "
               << "reboot";