[Atomics] Remove Atomics code stubs; use TF ops

src/compiler/code-assembler.h

Index: src/compiler/code-assembler.h
diff --git a/src/compiler/code-assembler.h b/src/compiler/code-assembler.h
index f70620ef1bf820ac5ca254bf9c18b7cc961375f8..c1175c94cdf6a0011dadf170220f1a589c96b81e 100644
--- a/src/compiler/code-assembler.h
+++ b/src/compiler/code-assembler.h
@@ -221,6 +221,7 @@ class CodeAssembler {
   // Load raw memory location.
   Node* Load(MachineType rep, Node* base);
   Node* Load(MachineType rep, Node* base, Node* index);
+  Node* AtomicLoad(MachineType rep, Node* base, Node* index);
 
   // Store value to raw memory location.
   Node* Store(MachineRepresentation rep, Node* base, Node* value);
@@ -243,6 +244,8 @@ class CodeAssembler {
 
   Node* TruncateFloat64ToInt32RoundToZero(Node* a);
   Node* TruncateFloat64ToInt32JavaScript(Node* a);
+  // No-op on 32-bit, otherwise zero extend.
+  Node* ChangeUint32ToWord(Node* value);
 
   // Projections
   Node* Projection(int index, Node* value);