Convert CHECK to DCHECK.

Now that we know this pathway is involved in the incorrect setting of
page scale factors for OOPIFs, convert this CHECK to a DCHECK.

TBR=wjmaclean@chromium.org

(cherry picked from commit cb6a710)

Bug: 859428
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I4d8805056546cc6ada3525e57d307dbcb27e6f55
Reviewed-on: https://chromium-review.googlesource.com/1146329
Reviewed-by: Fady Samuel <fsamuel@chromium.org>
Commit-Queue: James MacLean <wjmaclean@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#577351}
Reviewed-on: https://chromium-review.googlesource.com/1150842
Reviewed-by: James MacLean <wjmaclean@chromium.org>
Cr-Commit-Position: refs/branch-heads/3497@{#93}
Cr-Branched-From: 271eaf5-refs/heads/master@{#576753}

cc/trees/layer_tree_host_impl.cc

@@ -4584,10 +4584,10 @@ std::unique_ptr<ScrollAndScaleSet> LayerTreeHostImpl::ProcessScrollDeltas() {
   scroll_info->page_scale_delta =
       active_tree_->page_scale_factor()->PullDeltaForMainThread();
   // We should never process non-unit page_scale_delta for an OOPIF subframe.
-  // TODO(wjmaclean): Remove this check as a pre-condition to closing the bug.
+  // TODO(wjmaclean): Remove this DCHECK as a pre-condition to closing the bug.
   // https://crbug.com/845097
-  CHECK(!settings().is_layer_tree_for_subframe ||
-        scroll_info->page_scale_delta == 1.f);
+  DCHECK(!settings().is_layer_tree_for_subframe ||
+         scroll_info->page_scale_delta == 1.f);
   scroll_info->top_controls_delta =
       active_tree()->top_controls_shown_ratio()->PullDeltaForMainThread();
   scroll_info->elastic_overscroll_delta =