Clean up Canvas heuristics after display list 2d mode is removed

Bug: 776826
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I4c94e829690b37da7029fdf1105731fbf6c2b0b6
Reviewed-on: https://chromium-review.googlesource.com/809607Reviewed-by: Justin Novosad <junov@chromium.org>
Commit-Queue: Olivia Lai <xlai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521892}

third_party/WebKit/Source/platform/graphics/CanvasHeuristicParameters.h

@@ -10,25 +10,13 @@ namespace blink {
 namespace CanvasHeuristicParameters {
 
 enum {
-  // Layer promotion heuristic parameters
+  // Disable Deferral overdraw parameters
   //======================================
 
-  // FIXME (crbug.com/463239):
-  // The Layer promotion heuristics should go away after slimming paint
-  // is completely phased in and display list canvases are modified to
-  // use a lightweight layering primitive instead of the
-  // SkCanvas::saveLayer.
-
   // Heuristic: Canvases that are overdrawn beyond this factor in a
-  // single frame are promoted to a direct composited layer so that
-  // their contents not be re-rasterized by the compositor when the
-  // containing layer is the object of a paint invalidation.
+  // single frame will be disabled deferral.
   kExpensiveOverdrawThreshold = 10,
 
-  kComplexClipsAreExpensive = 1,
-
-  kBlurredShadowsAreExpensive = 1,
-
   // Disable Acceleration heuristic parameters
   //===========================================