Move left and right trimming of FixedArray into Heap.

src/heap/heap.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HEAP_HEAP_H_
 #define V8_HEAP_HEAP_H_
 
 #include <cmath>
 
 #include "src/allocation.h"
@@ skipping 682 matching lines @@
   // Indicies for direct access into argument objects.
   static const int kArgumentsLengthIndex = 0;
   // callee is only valid in sloppy mode.
   static const int kArgumentsCalleeIndex = 1;
 
   // Finalizes an external string by deleting the associated external
   // data and clearing the resource pointer.
   inline void FinalizeExternalString(String* string);
 
   // Initialize a filler object to keep the ability to iterate over the heap
-  // when shortening objects.
+  // when introducing gaps within pages.
   void CreateFillerObjectAt(Address addr, int size);
 
   bool CanMoveObjectStart(HeapObject* object);
 
+  // Indicates whether live bytes adjustment is triggered from within the GC
+  // code or from mutator code.
   enum InvocationMode { FROM_GC, FROM_MUTATOR };
 
-  // Maintain marking consistency for IncrementalMarking.
+  // Maintain consistency of live bytes during incremental marking.
   void AdjustLiveBytes(Address address, int by, InvocationMode mode);
 
+  // Trim the given array from the left. Note that this relocates the object
+  // start and hence is only valid if there is only a single reference to it.
+  FixedArrayBase* LeftTrimFixedArray(FixedArrayBase* obj, int elements_to_trim);
+
+  // Trim the given array from the right.
+  template<Heap::InvocationMode mode>
+  void RightTrimFixedArray(FixedArrayBase* obj, int elements_to_trim);
+
   // Converts the given boolean condition to JavaScript boolean value.
   inline Object* ToBoolean(bool condition);
 
   // Performs garbage collection operation.
   // Returns whether there is a chance that another major GC could
   // collect more garbage.
   inline bool CollectGarbage(
       AllocationSpace space, const char* gc_reason = NULL,
       const GCCallbackFlags gc_callback_flags = kNoGCCallbackFlags);
 
@@ skipping 1805 matching lines @@
   DisallowHeapAllocation no_allocation;  // i.e. no gc allowed.
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_HEAP_H_