Use exponential backoff for component extension reloads.

chrome/browser/background/background_contents_service.cc

Index: chrome/browser/background/background_contents_service.cc
diff --git a/chrome/browser/background/background_contents_service.cc b/chrome/browser/background/background_contents_service.cc
index 47a69eda6b586272eeffb8ca4a0479b31537ea22..52d401d5ecf1f37403302fe11cb02a187c7b7067 100644
--- a/chrome/browser/background/background_contents_service.cc
+++ b/chrome/browser/background/background_contents_service.cc
@@ -263,6 +263,18 @@ void ReloadExtension(const std::string& extension_id, Profile* profile) {
 const char kUrlKey[] = "url";
 const char kFrameNameKey[] = "name";
 
+// Defines the backoff policy used for attempting to reload extensions.
+const net::BackoffEntry::Policy kExtensionReloadBackoffPolicy = {
+  0,                // Initial errors to ignore before applying backoff.
+  3000,             // Initial delay: 3 seconds.
+  2,                // Multiply factor.
+  0.1,              // Fuzzing percentage.
+  -1,               // Maximum backoff time: -1 for no maximum.
+  -1,               // Entry lifetime: -1 to never discard.
+  false,            // Whether to always use initial delay. No-op as there are
+                    // no initial errors to ignore.
+};
+
 int BackgroundContentsService::restart_delay_in_ms_ = 3000;  // 3 seconds.
 
 BackgroundContentsService::BackgroundContentsService(
@@ -523,9 +535,33 @@ void BackgroundContentsService::OnExtensionUninstalled(
 void BackgroundContentsService::RestartForceInstalledExtensionOnCrash(
     const Extension* extension,
     Profile* profile) {
+  int restart_delay = restart_delay_in_ms_;
+
+  // If the extension was a component extension, use exponential backoff when
+  // attempting to reload.
+  if (extensions::Manifest::IsComponentLocation(extension->location())) {
+    ExtensionBackoffEntryMap::const_iterator it =
+        backoff_map_.find(extension->id());
+
+    // Create a BackoffEntry if this is the first time we try to reload this
+    // particular extension.
+    if (it == backoff_map_.end()) {
+      std::unique_ptr<net::BackoffEntry> backoff_entry(
+          new net::BackoffEntry(&kExtensionReloadBackoffPolicy));
+      backoff_map_.insert(

[Wez, 2016/09/01 21:47:58]

You're inserting a new entry into backoff_map_ here but never erase()ing it -
should it be cleaned-up similarly to content_map_, so that we can have a
destructor DCHECK(empty) as we do for that?

[apacible, 2016/09/02 00:20:32]

Good catch. I'll address this in a follow up CL.

+          std::pair<extensions::ExtensionId,
+                    std::unique_ptr<net::BackoffEntry>>(
+              extension->id(), std::move(backoff_entry)));
+    }
+
+    net::BackoffEntry* entry = backoff_map_[extension->id()].get();
+    entry->InformOfRequest(false);
+    restart_delay = entry->GetTimeUntilRelease().InMilliseconds();

[Wez, 2016/09/01 21:47:58]

When do we re-set the backoff for an extension, if ever?

e.g. if an extension happens to hit a crash every so often then won't the
restart delay still ramp up, over time, to some arbitrary level?

e.g. if WebRTC sometimes crashes the MR extension then after a dozen crashes the
Cast feature will seem to be completely broken?

[apacible, 2016/09/02 00:20:32]

We currently do not reset the backoff within the same browser session.

Chatted offline - it would make sense reset the backoff entry after the
background contents normally shuts down or after has been running continuously
for a fixed time (e.g. one minute).

+  }
+
   base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
       FROM_HERE, base::Bind(&ReloadExtension, extension->id(), profile),
-      base::TimeDelta::FromMilliseconds(restart_delay_in_ms_));
+      base::TimeDelta::FromMilliseconds(restart_delay));
 }
 
 // Loads all background contents whose urls have been stored in prefs.