Add KeepaliveImpulse to extension process manager.

extensions/browser/process_manager.h

Index: extensions/browser/process_manager.h
diff --git a/extensions/browser/process_manager.h b/extensions/browser/process_manager.h
index 669ebe78557e4bfb6d71e252a367e54179ad2977..8c93d3a1911d5c8c181a897dc6523ca3d71e545c 100644
--- a/extensions/browser/process_manager.h
+++ b/extensions/browser/process_manager.h
@@ -92,6 +92,11 @@ class ProcessManager : public content::NotificationObserver {
   void IncrementLazyKeepaliveCountForView(
       content::RenderViewHost* render_view_host);
 
+  // Keeps a background page alive. Unlike IncrementLazyKeepaliveCount, these
+  // impulses will only keep the page alive for a limited amount of time unless
+  // called regularly.
+  void KeepaliveImpulse(const Extension* extension);
+
   // Handles a response to the ShouldSuspend message, used for lazy background
   // pages.
   void OnShouldSuspendAck(const std::string& extension_id, int sequence_id);
@@ -164,6 +169,13 @@ class ProcessManager : public content::NotificationObserver {
   // Close the given |host| iff it's a background page.
   void CloseBackgroundHost(ExtensionHost* host);
 
+  // Internal implementation of DecrementLazyKeepaliveCount with an
+  // |extension_id| known to have a lazy background page.
+  int DecrementLazyKeepaliveCountById(std::string extension_id);
+
+  // Checks if keepalive impulses have occured, and adjusts keep alive count.
+  void OnKeepaliveImpulseCheck();
+
   // These are called when the extension transitions between idle and active.
   // They control the process of closing the background page when idle.
   void OnLazyBackgroundPageIdle(const std::string& extension_id,