cc: Use multiple PrepareTiles approaches

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 c55480fbb14443a00455f190f05c866ff2773ac8..765ed506b6ed8d22228716924213541760d19420 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -260,7 +260,6 @@ void PictureLayerImpl::AppendQuads(RenderPass* render_pass,
       viewport_rect_for_tile_priority_in_content_space_, max_contents_scale);
 
   size_t missing_tile_count = 0u;
-  size_t on_demand_missing_tile_count = 0u;
   only_used_low_res_last_append_quads_ = true;
   for (PictureLayerTilingSet::CoverageIterator iter(
            tilings_.get(), max_contents_scale,
@@ -276,8 +275,12 @@ void PictureLayerImpl::AppendQuads(RenderPass* render_pass,
     append_quads_data->visible_content_area +=
         visible_geometry_rect.width() * visible_geometry_rect.height();
 
+    bool raster_source_covers_tile = *iter;

[brianderson, 2015/05/16 02:39:57]

Enne, Vlad: Is this correct?

[vmpstr, 2015/05/18 17:20:48]

Not quite. We've talked about this offline a little bit, but I think we should
use CoversRect to detect this and we probably won't be able to get the number of
tiles out of this, so maybe just a bool for now.

[enne (OOO), 2015/05/18 21:40:50]

Yeah, false here means that the coverage iterator couldn't find tiles that were
ready to draw to cover it.  That could just mean that they weren't ready to
draw.  (It could theoretically mean that there weren't any tilings, but this
wouldn't happen in practice.)  It could mean that there weren't tiles at all,
and that usually implies that the raster source can't cover it.

We could get the number of tiles, but it'd kind of be a waste of work.  I like
vmpstr's idea of just one CoversRect and a bool.

     bool has_draw_quad = false;
-    if (*iter && iter->IsReadyToDraw()) {
+    if (!raster_source_covers_tile) {
+      // If there's no raster source, we will definitely checkerboard.
+      append_quads_data->num_tiles_missing_raster_source++;
+    } else if (iter->IsReadyToDraw()) {
       const TileDrawInfo& draw_info = iter->draw_info();
       switch (draw_info.mode()) {
         case TileDrawInfo::RESOURCE_MODE: {
@@ -366,13 +369,9 @@ void PictureLayerImpl::AppendQuads(RenderPass* render_pass,
   }
 
   if (missing_tile_count) {
-    TRACE_EVENT_INSTANT2("cc",
-                         "PictureLayerImpl::AppendQuads checkerboard",
-                         TRACE_EVENT_SCOPE_THREAD,
-                         "missing_tile_count",
-                         missing_tile_count,
-                         "on_demand_missing_tile_count",
-                         on_demand_missing_tile_count);
+    TRACE_EVENT_INSTANT1("cc", "PictureLayerImpl::AppendQuads checkerboard",
+                         TRACE_EVENT_SCOPE_THREAD, "missing_tile_count",
+                         missing_tile_count);
   }
 
   // Aggressively remove any tilings that are not seen to save memory. Note