[turbofan] Use new CodeAssembler::GetJSContextParameter.

src/fast-accessor-assembler.cc

 // Copyright 2015 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.
 
 #include "src/fast-accessor-assembler.h"
 
 #include "src/base/logging.h"
 #include "src/code-stub-assembler.h"
 #include "src/code-stubs.h"  // For CallApiCallbackStub.
 #include "src/handles-inl.h"
@@ skipping 166 matching lines @@
   ApiFunction callback_api_function(FUNCTION_ADDR(callback_function));
   ExternalReference callback(&callback_api_function,
                              ExternalReference::DIRECT_API_CALL, isolate());
 
   // Create & call API callback via stub.
   const int kJSParameterCount = 1;
   CallApiCallbackStub stub(isolate(), kJSParameterCount, true, true);
   CallInterfaceDescriptor descriptor = stub.GetCallInterfaceDescriptor();
   DCHECK_EQ(4, descriptor.GetParameterCount());
   DCHECK_EQ(0, descriptor.GetStackParameterCount());
-  // TODO(vogelheim): There is currently no clean way to retrieve the context
-  //     parameter for a stub and the implementation details are hidden in
-  //     compiler/*. The context_paramter is computed as:
-  //       Linkage::GetJSCallContextParamIndex(descriptor->JSParameterCount())
-  const int kContextParameter = 3;
-  Node* context = assembler_->Parameter(kContextParameter);
+  Node* context = assembler_->GetJSContextParameter();
   Node* target = assembler_->HeapConstant(stub.GetCode());
 
   Node* call = assembler_->CallStub(
       descriptor, target, context,
       assembler_->UndefinedConstant(),  // callee (there's no JSFunction)
       assembler_->UndefinedConstant(),  // call_data (undefined)
       assembler_->Parameter(0),  // receiver (same as holder in this case)
       assembler_->ExternalConstant(callback),  // API callback function
       FromId(arg));                            // JS argument, on stack
   return FromRaw(call);
@@ skipping 62 matching lines @@
 void FastAccessorAssembler::Clear() {
   for (auto label : labels_) {
     delete label;
   }
   nodes_.clear();
   labels_.clear();
 }
 
 }  // namespace internal
 }  // namespace v8