Migrate most uses of Isolate::current_zone to Thread::zone.

runtime/vm/bitmap.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_BITMAP_H_
 #define VM_BITMAP_H_
 
 #include "vm/allocation.h"
 #include "vm/isolate.h"
 #include "vm/zone.h"
 
 namespace dart {
 
 // Forward declarations.
 class RawStackmap;
 class Stackmap;
 
 
 // BitmapBuilder is used to build a bitmap. The implementation is optimized
 // for a dense set of small bit maps without a fixed upper bound (e.g: a
 // pointer map description of a stack).
 class BitmapBuilder : public ZoneAllocated {
  public:
   BitmapBuilder()
       : length_(0),
         data_size_in_bytes_(kInitialSizeInBytes),
-        data_(Isolate::Current()->current_zone()->Alloc<uint8_t>(
+        data_(Thread::Current()->zone()->Alloc<uint8_t>(
             kInitialSizeInBytes)) {
     memset(data_, 0, kInitialSizeInBytes);
   }
 
   intptr_t Length() const { return length_; }
   void SetLength(intptr_t length);
 
   // Get/Set individual bits in the bitmap, setting bits beyond the bitmap's
   // length increases the length and expands the underlying bitmap if
   // needed.
@@ skipping 33 matching lines @@
   // (up to length_) is allowed and they are assumed to be false.
   intptr_t data_size_in_bytes_;
   uint8_t* data_;
 
   DISALLOW_COPY_AND_ASSIGN(BitmapBuilder);
 };
 
 }  // namespace dart
 
 #endif  // VM_BITMAP_H_