AllocationProfiler: introduce allocation_profiler flag in V8 api.

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index 9aa14ee02594edec2bc7f0935374d922043fbed7..a18cb05cfcb6b79fb8139345c06fbc656b43fdbe 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -1132,6 +1132,19 @@ class Isolate {
     function_entry_hook_ = function_entry_hook;
   }
 
+  bool enable_allocation_profiler() {
+    ASSERT(!IsInitialized() || !initialized_from_snapshot());
+    // Fallback for release version.
+    if (IsInitialized() && initialized_from_snapshot())
+      return false;
+    allocation_profiler_ = true;
+    return true;
+  }
+
+  bool is_allocation_profiler_enabled() const {
+    return allocation_profiler_ || FLAG_enable_allocation_profiler;
+  }
+
   void* stress_deopt_count_address() { return &stress_deopt_count_; }
 
   inline RandomNumberGenerator* random_number_generator();
@@ -1373,6 +1386,7 @@ class Isolate {
 
   // Counts deopt points if deopt_every_n_times is enabled.
   unsigned int stress_deopt_count_;
+  bool allocation_profiler_;
 
   friend class ExecutionAccess;
   friend class HandleScopeImplementer;