cc: Use reverse spiral iterator in tiling eviction.

cc/layers/picture_layer_impl_perftest.cc

Index: cc/layers/picture_layer_impl_perftest.cc
diff --git a/cc/layers/picture_layer_impl_perftest.cc b/cc/layers/picture_layer_impl_perftest.cc
index aeea2bb7fee2f8f68623911711864c12755bb6df..5218abd450655d57658a2ba2505d14e393fac83d 100644
--- a/cc/layers/picture_layer_impl_perftest.cc
+++ b/cc/layers/picture_layer_impl_perftest.cc
@@ -122,21 +122,15 @@ class PictureLayerImplPerfTest : public testing::Test {
     host_impl_.SetViewportSize(viewport_size);
     host_impl_.pending_tree()->UpdateDrawProperties();
 
-    TreePriority priorities[] = {SAME_PRIORITY_FOR_BOTH_TREES,
-                                 SMOOTHNESS_TAKES_PRIORITY,
-                                 NEW_CONTENT_TAKES_PRIORITY};
-    int priority_count = 0;
     timer_.Reset();
     do {
       int count = num_tiles;
-      PictureLayerImpl::LayerEvictionTileIterator it(
-          pending_layer_, priorities[priority_count]);
+      PictureLayerImpl::LayerEvictionTileIterator it(pending_layer_);
       while (count--) {
         ASSERT_TRUE(it) << "count: " << count;
         ASSERT_TRUE(*it != nullptr) << "count: " << count;
         ++it;
       }
-      priority_count = (priority_count + 1) % arraysize(priorities);
       timer_.NextLap();
     } while (!timer_.HasTimeLimitExpired());
 
@@ -155,15 +149,9 @@ class PictureLayerImplPerfTest : public testing::Test {
         gfx::ScrollOffset(viewport.x(), viewport.y()));
     host_impl_.pending_tree()->UpdateDrawProperties();
 
-    TreePriority priorities[] = {SAME_PRIORITY_FOR_BOTH_TREES,
-                                 SMOOTHNESS_TAKES_PRIORITY,
-                                 NEW_CONTENT_TAKES_PRIORITY};
-    int priority_count = 0;
     timer_.Reset();
     do {
-      PictureLayerImpl::LayerEvictionTileIterator it(
-          pending_layer_, priorities[priority_count]);
-      priority_count = (priority_count + 1) % arraysize(priorities);
+      PictureLayerImpl::LayerEvictionTileIterator it(pending_layer_);
       timer_.NextLap();
     } while (!timer_.HasTimeLimitExpired());