remove byte-accounting assert for crbug.com/536163

The change https://codereview.chromium.org/1274453002 is causing a breakage
on the Chrome OS builds. It is not clear how to easily revert because there is
a following on dependent change (https://codereview.chromium.org/1351983002) am
I am not too familiar with the revert process.

The simplest revert is to remove the DCHECK.

BUG=chromium:536163
LOG=n
NOTRY=true
R=machenbach@chromium.org, cmumford@chromium.org, hpayer@chromium.org

Review URL: https://codereview.chromium.org/1372693002 .

Cr-Commit-Position: refs/heads/master@{#30959}

src/heap/incremental-marking.cc

@@ -901,7 +901,8 @@ intptr_t IncrementalMarking::Step(intptr_t allocated_bytes,
                                   CompletionAction action,
                                   ForceMarkingAction marking,
                                   ForceCompletionAction completion) {
-  DCHECK(allocated_bytes >= 0);
+  // Temporarily removed for crbug.com/536163
+  // DCHECK(allocated_bytes >= 0);
 
   if (heap_->gc_state() != Heap::NOT_IN_GC || !FLAG_incremental_marking ||
       (state_ != SWEEPING && state_ != MARKING)) {