Disentangle assembler from isolate.

src/arm64/code-stubs-arm64.h

 // Copyright 2013 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_ARM64_CODE_STUBS_ARM64_H_
 #define V8_ARM64_CODE_STUBS_ARM64_H_
 
 namespace v8 {
 namespace internal {
 
@@ skipping 112 matching lines @@
 
   // We patch the two first instructions of the stub back and forth between an
   // adr and branch when we start and stop incremental heap marking.
   // The branch is
   //   b label
   // The adr is
   //   adr xzr label
   // so effectively a nop.
   static void Patch(Code* stub, Mode mode) {
     // We are going to patch the two first instructions of the stub.
-    PatchingAssembler patcher(
-        stub->GetIsolate(),
-        reinterpret_cast<Instruction*>(stub->instruction_start()), 2);
+    PatchingAssembler patcher(stub->GetIsolate(), stub->instruction_start(), 2);
     Instruction* instr1 = patcher.InstructionAt(0);
     Instruction* instr2 = patcher.InstructionAt(kInstructionSize);
     // Instructions must be either 'adr' or 'b'.
     DCHECK(instr1->IsPCRelAddressing() || instr1->IsUncondBranchImm());
     DCHECK(instr2->IsPCRelAddressing() || instr2->IsUncondBranchImm());
     // Retrieve the offsets to the labels.
     auto offset_to_incremental_noncompacting =
         static_cast<int32_t>(instr1->ImmPCOffset());
     auto offset_to_incremental_compacting =
         static_cast<int32_t>(instr2->ImmPCOffset());
@@ skipping 196 matching lines @@
   class LookupModeBits: public BitField<LookupMode, 0, 1> {};
 
   DEFINE_NULL_CALL_INTERFACE_DESCRIPTOR();
   DEFINE_PLATFORM_CODE_STUB(NameDictionaryLookup, PlatformCodeStub);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_ARM64_CODE_STUBS_ARM64_H_