Fix the failure when enabling v8 profiler or vtune profiler in chromium.

   When enabling the v8 profiler (Using the following command parameters: --js-flags=--prof)
   or vtune profiling in chromium. it will break. This failure is introduced by this CL:
   https://codereview.chromium.org/1218863002.

   The reason is that V8 will enable the JITted code logging if --prof is set for V8. And under
   this condition, the function Logger::LogCodeObjects() will be invoked and it will trigger a
   mark-compact GC when deserializing the snapshot. This GC will use MemoryReducer to post a
   delay task by invoking V8Platform::CallDelayedOnForegroundThread() function. But at this point
   V8 isolation is still under initialization and the PerIsolationData of this isolation has not
   been created. (isolation_holder.cc:39~40 line). This leads to V8Platform::CallDelayedOnForegroundThread()
   failure because of segment fault.

   According to my understanding, I proposed the following fix. If the heap deserialization has not
   be completed, it does not post the delay task for next GC.

BUG=

Review URL: https://codereview.chromium.org/1270493002

Cr-Commit-Position: refs/heads/master@{#29937}

src/heap/heap.cc

@@ -966,7 +966,9 @@ bool Heap::CollectGarbage(GarbageCollector collector, const char* gc_reason,
           (committed_memory_before - committed_memory_after) > MB ||
           HasHighFragmentation(used_memory_after, committed_memory_after) ||
           (detached_contexts()->length() > 0);
-      memory_reducer_.NotifyMarkCompact(event);
+      if (deserialization_complete_) {
+        memory_reducer_.NotifyMarkCompact(event);
+      }
     }
 
     tracer()->Stop(collector);