ui: Cache the output of View::OnPaint when the View isn't invalid.

ui/views/view.cc

Index: ui/views/view.cc
diff --git a/ui/views/view.cc b/ui/views/view.cc
index 78659caf418cd1b5ee47d40b98e1841a3e4f659b..e5e47198fff67b24d2533a66f701dd084e56e289 100644
--- a/ui/views/view.cc
+++ b/ui/views/view.cc
@@ -748,6 +748,7 @@ void View::Paint(const ui::PaintContext& parent_context) {
   ui::PaintContext context =
       parent_context.CloneWithPaintOffset(offset_to_parent);
 
+  bool is_invalidated = true;

[sky, 2015/04/23 16:29:00]

is_invalid?

   if (context.CanCheckInvalidated()) {
 #if DCHECK_IS_ON()
     gfx::Vector2d offset;
@@ -770,10 +771,12 @@ void View::Paint(const ui::PaintContext& parent_context) {
 
     // If the View wasn't invalidated, don't waste time painting it, the output
     // would be culled.
-    if (!context.IsRectInvalidated(GetLocalBounds()))
-      return;
+    is_invalidated = context.IsRectInvalidated(GetLocalBounds());

[sky, 2015/04/23 16:29:00]

nit: IsRectInvalidated() sounds like it is modifying context, when it's just
querying. IsRectInvalid() seems like a better name.

[danakj, 2015/04/23 16:34:09]

Hm, I disagree. "Invalidated" means that SchedulePaint was called, and "IsFoo"
is a query about Foo. But it sounds like you prefer "Invalid" over "Invalidated"
throughout for this concept of "did SchedulePaint happen". We call this
"invalidated" everywhere in cc/ so I'm just used to that. I can use invalid here
(though slightly prefer consistency).

   }
 
+  if (!is_invalidated && context.EarlyOutOfPaintingWhenNotInvalidated())
+    return;
+
   TRACE_EVENT1("views", "View::Paint", "class", GetClassName());
 
   // If the view is backed by a layer, it should paint with itself as the origin
@@ -803,8 +806,8 @@ void View::Paint(const ui::PaintContext& parent_context) {
     clip_transform_recorder->Transform(transform_from_parent);
   }
 
-  {
-    ui::PaintRecorder recorder(context);
+  if (is_invalidated || !paint_cache_.UseCache(context)) {
+    ui::PaintRecorder recorder(context, &paint_cache_);
     gfx::Canvas* canvas = recorder.canvas();
     gfx::ScopedCanvas scoped_canvas(canvas);