A speculative Revert for r165872 - Remove static thread pointers from CC, attempt 2

cc/layer_sorter_unittest.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 
 #include "cc/layer_sorter.h"
 
 #include "cc/layer_impl.h"
 #include "cc/math_util.h"
@@ skipping 171 matching lines @@
     bool clipped = false;
     MathUtil::mapQuad(perspectiveMatrix * transformB, testQuad, clipped);
     ASSERT_TRUE(clipped);
 
     overlapResult = LayerSorter::checkOverlap(&layerA, &layerB, zThreshold, weight);
     EXPECT_EQ(LayerSorter::ABeforeB, overlapResult);
 }
 
 TEST(LayerSorterTest, verifyExistingOrderingPreservedWhenNoZDiff)
 {
+    DebugScopedSetImplThread thisScopeIsOnImplThread;
+
     // If there is no reason to re-sort the layers (i.e. no 3d z difference), then the
     // existing ordering provided on input should be retained. This test covers the fix in
     // https://bugs.webkit.org/show_bug.cgi?id=75046. Before this fix, ordering was
     // accidentally reversed, causing bugs in z-index ordering on websites when
     // preserves3D triggered the LayerSorter.
 
     // Input list of layers: [1, 2, 3, 4, 5].
     // Expected output: [3, 4, 1, 2, 5].
     //    - 1, 2, and 5 do not have a 3d z difference, and therefore their relative ordering should be retained.
     //    - 3 and 4 do not have a 3d z difference, and therefore their relative ordering should be retained.
@@ skipping 54 matching lines @@
 
     ASSERT_EQ(static_cast<size_t>(5), layerList.size());
     EXPECT_EQ(3, layerList[0]->id());
     EXPECT_EQ(4, layerList[1]->id());
     EXPECT_EQ(1, layerList[2]->id());
     EXPECT_EQ(2, layerList[3]->id());
     EXPECT_EQ(5, layerList[4]->id());
 }
 
 } // namespace