Reduce CPU usage of download shelf UI. (both MD and pre-MD shelves)

chrome/browser/ui/views/download/download_item_view.cc

Index: chrome/browser/ui/views/download/download_item_view.cc
diff --git a/chrome/browser/ui/views/download/download_item_view.cc b/chrome/browser/ui/views/download/download_item_view.cc
index a11d7ed032d861c5e6132e546fb860da4064ce00..6e3e8b85ad157100b3ad4ce7dca76335d9d73120 100644
--- a/chrome/browser/ui/views/download/download_item_view.cc
+++ b/chrome/browser/ui/views/download/download_item_view.cc
@@ -236,21 +236,16 @@ DownloadItemView::~DownloadItemView() {
 // Progress animation handlers.
 
 void DownloadItemView::StartDownloadProgress() {
-  if (progress_timer_.IsRunning())
+  if (progress_start_time_ != base::TimeTicks())
     return;
   progress_start_time_ = base::TimeTicks::Now();
-  progress_timer_.Start(
-      FROM_HERE,
-      base::TimeDelta::FromMilliseconds(DownloadShelf::kProgressRateMs),

[asanka, 2015/12/18 03:39:16]

Would you be willing to get rid of this 30ms timer on Mac as well?

[Evan Stade, 2015/12/18 19:01:38]

yea I meant to look at doing that, thanks for reminding me. I don't have a mac
to verify it doesn't break, though.

[Evan Stade, 2015/12/29 18:50:49]

This seems complicated enough that I'd want someone with an OSX build to have a
look at doing it.

-      base::Bind(&DownloadItemView::SchedulePaint, base::Unretained(this)));
 }
 
 void DownloadItemView::StopDownloadProgress() {
-  if (!progress_timer_.IsRunning())
+  if (progress_start_time_ == base::TimeTicks())
     return;
   previous_progress_elapsed_ += base::TimeTicks::Now() - progress_start_time_;
   progress_start_time_ = base::TimeTicks();
-  progress_timer_.Stop();
 }
 
 void DownloadItemView::OnExtractIconComplete(gfx::Image* icon_bitmap) {
@@ -284,6 +279,7 @@ void DownloadItemView::OnDownloadUpdated(DownloadItem* download_item) {
       case DownloadItem::IN_PROGRESS:
         download()->IsPaused() ?
             StopDownloadProgress() : StartDownloadProgress();
+        SchedulePaint();
         LoadIconIfItemPathChanged();
         break;
       case DownloadItem::INTERRUPTED:
@@ -327,11 +323,6 @@ void DownloadItemView::OnDownloadUpdated(DownloadItem* download_item) {
   }
 
   UpdateAccessibleName();
-
-  // We use the parent's (DownloadShelfView's) SchedulePaint, since there
-  // are spaces between each DownloadItemView that the parent is responsible
-  // for painting.
-  shelf_->SchedulePaint();
 }
 
 void DownloadItemView::OnDownloadDestroyed(DownloadItem* download) {