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

runtime/vm/assembler.cc

 // 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.
 
 #include "vm/assembler.h"
 
 #include "platform/utils.h"
 #include "vm/cpu.h"
 #include "vm/heap.h"
 #include "vm/memory_region.h"
 #include "vm/os.h"
 #include "vm/zone.h"
 
 namespace dart {
 
 DEFINE_FLAG(bool, code_comments, false,
             "Include comments into code and disassembly");
 #if defined(TARGET_ARCH_ARM) || defined(TARGET_ARCH_MIPS)
 DEFINE_FLAG(bool, use_far_branches, false,
             "Enable far branches for ARM and MIPS");
 #endif
 
 DECLARE_FLAG(bool, disassemble);
 DECLARE_FLAG(bool, disassemble_optimized);
 
 static uword NewContents(intptr_t capacity) {
-  Zone* zone = Isolate::Current()->current_zone();
+  Zone* zone = Thread::Current()->zone();
   uword result = zone->AllocUnsafe(capacity);
 #if defined(DEBUG)
   // Initialize the buffer with kBreakPointInstruction to force a break
   // point if we ever execute an uninitialized part of the code buffer.
   Assembler::InitializeMemoryWithBreakpoints(result, capacity);
 #endif
   return result;
 }
 
 
@@ skipping 289 matching lines @@
       result.SetObjectAt(i, *object_pool_[i].obj_);
     } else {
       result.SetRawValueAt(i, object_pool_[i].raw_value_);
     }
   }
   return result.raw();
 }
 
 
 }  // namespace dart