WIP Hittest Component.

cc/surfaces/surface_aggregator.cc

Index: cc/surfaces/surface_aggregator.cc
diff --git a/cc/surfaces/surface_aggregator.cc b/cc/surfaces/surface_aggregator.cc
index f0e73f8a06a835fdb22d2368cad0415218225dd2..bde4f820a843b2c03f426f6873e9808798cde9e1 100644
--- a/cc/surfaces/surface_aggregator.cc
+++ b/cc/surfaces/surface_aggregator.cc
@@ -760,8 +760,10 @@ gfx::Rect SurfaceAggregator::PrewalkTree(const SurfaceId& surface_id,
   CHECK(debug_weak_this.get());
   // TODO(staraz): It shouldn't need to call the callback when the damage is
   // from |surface| and not from |child_surfaces|.
-  if (!damage_rect.IsEmpty())
+  if (!damage_rect.IsEmpty()) {

[rjkroege, 2017/06/07 17:16:44]

Would we ever want to adjust the HitTestData without altering the display?

[gklassen, 2017/06/07 20:04:43]

not sure what you mean?

[rjkroege, 2017/06/07 20:22:55]

It was idle speculation: would we want to alter the HTD without also altering
the CF?

Also: I don't really understand SurfaceAggregator well enough to know if this is
the right place to invoke the observers.

Given that this is on the critical path, we want to make sure that the observers
are efficient.

[gklassen, 2017/06/08 17:09:21]

OIC.  Currently the only mechanism we have contemplated to update hittest data
is tied to SubmitCompositorFrame - we could make changes to support updates at
any time, but currently I'm unaware of possible causes ( although I will have a
much better perspective after we are generating real hit test data and we can
keep this in mind ). 

I selected this entry with some over the shoulder help from some in the group. 
Is there a good set of reviewers who understand SurfaceAggregator and could help
review if this is a good place to invoke observers? ( We will also know much
more after we try it in context with real hittestdata ).

     surface->RunWillDrawCallback(damage_rect);
+    manager_->SurfaceWillDraw(surface->surface_id());
+  }
 
   CHECK(debug_weak_this.get());
   for (const auto& render_pass : frame.render_pass_list) {