Filter out redundant jumplist updates.

chrome/browser/jumplist_win.cc

Index: chrome/browser/jumplist_win.cc
diff --git a/chrome/browser/jumplist_win.cc b/chrome/browser/jumplist_win.cc
index 22a73e61f4f8b40c59006335369f5fbbd332b406..a8fd822f4fd6ad3a14b4fed5fc4d04402738d2df 100644
--- a/chrome/browser/jumplist_win.cc
+++ b/chrome/browser/jumplist_win.cc
@@ -46,6 +46,10 @@ using content::BrowserThread;
 
 namespace {
 
+// Delay jumplist update tasks to allow collapsing of redundant
+// update requests.
+const int kDelayMSForJumplistUpdate = 1500;

[jochen (gone - plz use gerrit), 2015/03/31 10:28:52]

nit. it's more common to have the unit last (kDelayForJumplistUpdateInMS)

[brucedawson, 2015/06/03 17:57:16]

Done.

+
 // Append the common switches to each shell link.
 void AppendCommonSwitches(ShellLinkItem* shell_link) {
   const char* kSwitchNames[] = { switches::kUserDataDir };
@@ -445,11 +449,20 @@ void JumpList::PostRunUpdate() {
       profile_ ? IncognitoModePrefs::GetAvailability(profile_->GetPrefs())
                : IncognitoModePrefs::ENABLED;
 
-  BrowserThread::PostTask(
+  // Post the JumpListIcons update request with a brief delay.
+  BrowserThread::PostDelayedTask(
       BrowserThread::FILE, FROM_HERE,
       base::Bind(&JumpList::RunUpdateOnFileThread,
                  this,
-                 incognito_availability));
+                 incognito_availability),
+                 base::TimeDelta::FromMilliseconds(kDelayMSForJumplistUpdate));
+
+  {
+    // Record the request time (after posting the task) to allow filtering
+    // out redundant update requests.
+    base::AutoLock auto_lock(list_lock_);
+    lastUpdateRequested_ = base::TimeTicks::NowFromSystemTraceTime();
+  }
 }
 
 void JumpList::RunUpdateOnFileThread(
@@ -464,6 +477,19 @@ void JumpList::RunUpdateOnFileThread(
     if (!icon_urls_.empty())
       return;
 
+    // If we get a storm of update requests then we can skip most of the
+    // updates. Any update that starts after the last request will have
+    // done all the necessary work. This addresses this scenario:
+    // t=10.0: PostRunUpdate
+    // t=10.1: PostRunUpdate
+    // t=10.5: RunUpdateOnFileThread
+    // t=10.6: RunUpdateOnFileThread -- no update necessary!
+    // If the times are equal the meaning is ambiguous, so only return if
+    // the update-start time is clearly greater.
+    if (lastUpdateStarted_ > lastUpdateRequested_)
+      return;
+    lastUpdateStarted_ = base::TimeTicks::NowFromSystemTraceTime();
+
     // Make local copies of lists so we can release the lock.
     local_most_visited_pages = most_visited_pages_;
     local_recently_closed_pages = recently_closed_pages_;