[Blink] Remove lingering TODO(crbug.com/756265) which no longer applies

BUG=756265

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I92274be4c9ed75922d675c7c027c2fcce54709a2
Reviewed-on: https://chromium-review.googlesource.com/1006398Reviewed-by: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Tien-Ren Chen <trchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549943}

third_party/blink/renderer/core/paint/compositing/composited_layer_mapping.cc

@@ -642,9 +642,6 @@ void CompositedLayerMapping::
     return;
   }
 
-  // TODO(crbug.com/756265): Our composited in-flow descendants expect to
-  // inherit our clip, and we shouldn't omit rounded clip if some descendants
-  // could be clipped by it.
   FloatRect bounds_in_ancestor_space =
       GetLayoutObject()
           .LocalToAncestorQuad(FloatRect(composited_bounds_),