cc: Early out of UpdateTiles for resoureceless draw

cc/layers/picture_layer_impl.cc

Index: cc/layers/picture_layer_impl.cc
diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index 04ac9ad59a79c3a74c35881d8e1e9a5ed4096ee6..6b39260e6281e190e474e9d642a9ba91fe011f47 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -413,11 +413,6 @@ void PictureLayerImpl::AppendQuads(RenderPass* render_pass,
 }
 
 bool PictureLayerImpl::UpdateTiles(bool resourceless_software_draw) {
-  if (!resourceless_software_draw) {
-    visible_rect_for_tile_priority_ = visible_layer_rect();
-    screen_space_transform_for_tile_priority_ = ScreenSpaceTransform();
-  }
-
   if (!CanHaveTilings()) {
     ideal_page_scale_ = 0.f;
     ideal_device_scale_ = 0.f;
@@ -435,6 +430,9 @@ bool PictureLayerImpl::UpdateTiles(bool resourceless_software_draw) {
   if (layer_tree_impl()->IsActiveTree())
     CleanUpTilingsOnActiveLayer(last_append_quads_tilings_);
 
+  if (resourceless_software_draw)

[vmpstr, 2016/01/25 23:44:05]

It's a bit of an awkward pattern:

f(bool foo) {
  ...
  if (foo)
    return;
  ...
}

It feels like it should be 

f() {
 ...
} 

and 

g() { 
 ...
}

and the caller can just

f();
if (!foo)
 g();


The problem of course is how to name and separate these two functions so that
they still make sense. Other than that, there's only one non-test callsite for
this, so I think the split would make sense. What do you think?

[boliu, 2016/01/26 00:01:02]

Maybe don't need the split at all, and just skip everything?

Resourceless draw doesn't need to call CleanUpTilingsOnActiveLayer since
resourceless draw does not affect |last_append_quads_tilings_|.

I'm less sure about the !CanHaveTilings() block. According to
SanityCheckTilingState, |tilings_| is supposed to be empty already. Do the ideal
scales matter in that case?

+    return false;
+
   UpdateIdealScales();
 
   if (!raster_contents_scale_ || ShouldAdjustRasterScale()) {
@@ -494,17 +492,17 @@ bool PictureLayerImpl::UpdateTiles(bool resourceless_software_draw) {
 }
 
 void PictureLayerImpl::UpdateViewportRectForTilePriorityInContentSpace() {
-  // If visible_rect_for_tile_priority_ is empty or
-  // viewport_rect_for_tile_priority is set to be different from the device
-  // viewport, try to inverse project the viewport into layer space and use
-  // that. Otherwise just use visible_rect_for_tile_priority_
-  gfx::Rect visible_rect_in_content_space = visible_rect_for_tile_priority_;
+  // If visible_layer_rect() is empty or viewport_rect_for_tile_priority is
+  // set to be different from the device viewport, try to inverse project the
+  // viewport into layer space and use that. Otherwise just use
+  // visible_layer_rect().
+  gfx::Rect visible_rect_in_content_space = visible_layer_rect();
   gfx::Rect viewport_rect_for_tile_priority =
       layer_tree_impl()->ViewportRectForTilePriority();
   if (visible_rect_in_content_space.IsEmpty() ||
       layer_tree_impl()->DeviceViewport() != viewport_rect_for_tile_priority) {
     gfx::Transform view_to_layer(gfx::Transform::kSkipInitialization);
-    if (screen_space_transform_for_tile_priority_.GetInverse(&view_to_layer)) {
+    if (ScreenSpaceTransform().GetInverse(&view_to_layer)) {
       // Transform from view space to content space.
       visible_rect_in_content_space = MathUtil::ProjectEnclosingClippedRect(
           view_to_layer, viewport_rect_for_tile_priority);