Allow fallback from https to http for component update checks.

components/update_client/update_engine.cc

Index: components/update_client/update_engine.cc
diff --git a/components/update_client/update_engine.cc b/components/update_client/update_engine.cc
index 06cf6eb723d7f921f0427890935e00651baa9204..20f9a6acf1e28f30be484fe7548aff4527dc37f9 100644
--- a/components/update_client/update_engine.cc
+++ b/components/update_client/update_engine.cc
@@ -9,6 +9,7 @@
 #include "base/location.h"
 #include "base/stl_util.h"
 #include "base/thread_task_runner_handle.h"
+#include "base/time/time.h"
 #include "components/update_client/action_update_check.h"
 #include "components/update_client/configurator.h"
 #include "components/update_client/crx_update_item.h"
@@ -36,8 +37,8 @@ UpdateContext::UpdateContext(
       blocking_task_runner(config->GetSequencedTaskRunner()),
       update_checker_factory(update_checker_factory),
       crx_downloader_factory(crx_downloader_factory),
-      ping_manager(ping_manager) {
-}
+      ping_manager(ping_manager),
+      retry_after_sec_(0) {}
 
 UpdateContext::~UpdateContext() {
   STLDeleteElements(&update_items);
@@ -84,6 +85,12 @@ void UpdateEngine::Update(
     const CompletionCallback& callback) {
   DCHECK(thread_checker_.CalledOnValidThread());
 
+  if (IsThrottled(is_foreground)) {
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE, base::Bind(callback, Error::ERROR_UPDATE_RETRY_LATER));
+    return;
+  }
+
   scoped_ptr<UpdateContext> update_context(new UpdateContext(
       config_, is_foreground, ids, crx_data_callback,
       notify_observers_callback_, callback, update_checker_factory_,
@@ -109,6 +116,18 @@ void UpdateEngine::UpdateComplete(UpdateContext* update_context, int error) {
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(update_contexts_.find(update_context) != update_contexts_.end());
 
+  const int throttle_sec(update_context->retry_after_sec_);
+  DCHECK_LE(throttle_sec, 24 * 60 * 60);
+
+  // Only positive values for throttle_sec are effective. 0 means that no
+  // throttling occurs and has the effect of resetting the member.
+  // Negative values are not trusted and are ignored.
+  if (throttle_sec >= 0)
+    throttle_updates_until_ =
+        throttle_sec
+            ? base::Time::Now() + base::TimeDelta::FromSeconds(throttle_sec)
+            : base::Time();
+
   auto callback = update_context->callback;
 
   update_contexts_.erase(update_context);
@@ -117,4 +136,16 @@ void UpdateEngine::UpdateComplete(UpdateContext* update_context, int error) {
   callback.Run(error);
 }
 
+bool UpdateEngine::IsThrottled(bool is_foreground) const {
+  if (is_foreground || throttle_updates_until_.is_null())
+    return false;
+
+  const auto now(base::Time::Now());
+
+  // Throttle the calls in the interval (t - 1 day, t) to limit the effect of
+  // unset clocks or clock drift.
+  return throttle_updates_until_ - base::TimeDelta::FromDays(1) < now &&
+         now < throttle_updates_until_;
+}
+
 }  // namespace update_client