Switch cc to std::unordered_*.

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 2399289de05203c768f2b7755d83270ebfcb6618..532af762753c4210081057cc5af7f9718588e293 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -11,9 +11,10 @@
 #include <limits>
 #include <map>
 #include <set>
+#include <unordered_map>
+#include <utility>
 
 #include "base/auto_reset.h"
-#include "base/containers/hash_tables.h"
 #include "base/containers/small_map.h"
 #include "base/json/json_writer.h"
 #include "base/metrics/histogram.h"
@@ -1185,7 +1186,8 @@ void LayerTreeHostImpl::RemoveRenderPasses(FrameData* frame) {
   std::set<RenderPassId> pass_exists;
   // A set of RenderPassDrawQuads that we have seen (stored by the RenderPasses
   // they refer to).
-  base::SmallMap<base::hash_map<RenderPassId, int>> pass_references;
+  base::SmallMap<std::unordered_map<RenderPassId, int, RenderPassIdHash>>
+      pass_references;
 
   // Iterate RenderPasses in draw order, removing empty render passes (except
   // the root RenderPass).
@@ -3288,9 +3290,12 @@ void LayerTreeHostImpl::RegisterScrollbarAnimationController(
     return;
   if (ScrollbarAnimationControllerForId(scroll_layer_id))
     return;
-  scrollbar_animation_controllers_.add(
+  // TODO(davidben): Is this the same as using operator[]? The check above

[danakj, 2016/01/14 21:12:32]

You're worried for the case where the scroll_layer_id exists in the map, but the
scoped_ptr value is null? I think that won't happen. The only place the
controller is changed is here and unregister. So it either sets a pointer or
erases the key.

[davidben, 2016/01/14 21:28:19]

I'm worried about the case where scroll_layer_id exists in the map.
ScopedPtrHashMap::add acts like unordered_map::insert in that it apparently does
nothing if the key already exists, whereas assigning to operator[] will always
modify the map.

I would be pretty surprised if this code actively wants this behavior, but I
wasn't sure so left it like this to ask you about. Will switch to operator[] if
that's the desired behavior, although it is a little odd that the check on line
3291 isn't quiiiite the right check.

[danakj, 2016/01/14 21:31:54]

Yah it is a bit awkward. I think operator[] will be fine tho, we shouldn't have
null values in the map since the only place that sets them is here and
CreateScrollbarAnimationController won't return null (without hitting a DCHECK).

[davidben, 2016/01/21 01:33:58]

Done.

+  // doesn't quite work if scroll_layer_id gets modified in
+  // ScrollbarAnimationControllerForId.
+  scrollbar_animation_controllers_.insert(std::make_pair(
       scroll_layer_id,
-      active_tree_->CreateScrollbarAnimationController(scroll_layer_id));
+      active_tree_->CreateScrollbarAnimationController(scroll_layer_id)));
 }
 
 void LayerTreeHostImpl::UnregisterScrollbarAnimationController(
@@ -3307,7 +3312,7 @@ LayerTreeHostImpl::ScrollbarAnimationControllerForId(
   auto i = scrollbar_animation_controllers_.find(scroll_layer_id);
   if (i == scrollbar_animation_controllers_.end())
     return nullptr;
-  return i->second;
+  return i->second.get();
 }
 
 void LayerTreeHostImpl::PostDelayedScrollbarAnimationTask(