Remove V8.ZoneSegmentBytes.

1) It's unused. 2) Since Zones can be used on a background thread, the Zone
cannot just access this counter from the Isolate, so keeping this counter up to
date would require extra work. Better to just remove it.

BUG=431860
LOG=n
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/716793002

Cr-Commit-Position: refs/heads/master@{#25263}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25263 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/counters.h

@@ -489,7 +489,6 @@ class HistogramTimerScope BASE_EMBEDDED {
   SC(for_in, V8.ForIn)                                                         \
   SC(enum_cache_hits, V8.EnumCacheHits)                                        \
   SC(enum_cache_misses, V8.EnumCacheMisses)                                    \
-  SC(zone_segment_bytes, V8.ZoneSegmentBytes)                                  \
   SC(fast_new_closure_total, V8.FastNewClosureTotal)                           \
   SC(fast_new_closure_try_optimized, V8.FastNewClosureTryOptimized)            \
   SC(fast_new_closure_install_optimized, V8.FastNewClosureInstallOptimized)    \

src/zone-inl.h

@@ -31,7 +31,6 @@ bool Zone::excess_allocation() {
 
 void Zone::adjust_segment_bytes_allocated(int delta) {
   segment_bytes_allocated_ += delta;
-  isolate_->counters()->zone_segment_bytes()->Set(segment_bytes_allocated_);
 }