Revert "[PE] Change CHECK to LOG(WARNING) in PaintController::FindOutOfOrderCachedItemForward"

This reverts commit 8bc8a796.

Reason for revert: It broke some tests on waterfall bots.
 
Original change's description:
> [PE] Change CHECK to LOG(WARNING) in PaintController::FindOutOfOrderCachedItemForward
> 
> The situation doesn't cause corrupted rendering but just slightly
> affects performance. It's fine not to DCHECK given that the situation
> is rare.
> 
> Bug: 805024
> Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
> Change-Id: Iac8cd617d5df51da2516fc6a9df1308a0daaedd0
> Reviewed-on: https://chromium-review.googlesource.com/990074
> Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
> Reviewed-by: Philip Rogers <pdr@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#547923}

TBR=wangxianzhu@chromium.org,pdr@chromium.org

Change-Id: If8c1dcd5e7d2f89ba688eadec9d3d047df777055
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 805024
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Reviewed-on: https://chromium-review.googlesource.com/994338Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547980}

third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp

@@ -480,7 +480,7 @@ size_t PaintController::FindOutOfOrderCachedItemForward(
 #endif
     // Ensure our paint invalidation tests don't trigger the less performant
     // situation which should be rare.
-    LOG(WARNING) << "Can't find cached display item: " << id.client.DebugName()
+    CHECK(false) << "Can't find cached display item: " << id.client.DebugName()
                  << " " << id.ToString();
   }
   return kNotFound;