[stubs] Use a single slot for context globals.

src/full-codegen/arm64/full-codegen-arm64.cc

Index: src/full-codegen/arm64/full-codegen-arm64.cc
diff --git a/src/full-codegen/arm64/full-codegen-arm64.cc b/src/full-codegen/arm64/full-codegen-arm64.cc
index 78681b4683499368feddee72f33b80214838583d..40af62cf1953f2b95a2b129b24c3a722eef8b3ea 100644
--- a/src/full-codegen/arm64/full-codegen-arm64.cc
+++ b/src/full-codegen/arm64/full-codegen-arm64.cc
@@ -1397,7 +1397,6 @@ void FullCodeGenerator::EmitGlobalVariableLoad(VariableProxy* proxy,
   if (var->IsGlobalSlot()) {
     DCHECK(var->index() > 0);
     DCHECK(var->IsStaticGlobalObjectProperty());
-    // Each var occupies two slots in the context: for reads and writes.
     int const slot = var->index();
     int const depth = scope()->ContextChainLength(var->scope());
     if (depth <= LoadGlobalViaContextStub::kMaximumDepth) {
@@ -2399,8 +2398,7 @@ void FullCodeGenerator::EmitVariableAssignment(Variable* var, Token::Value op,
     // Global var, const, or let.
     DCHECK(var->index() > 0);
     DCHECK(var->IsStaticGlobalObjectProperty());
-    // Each var occupies two slots in the context: for reads and writes.
-    int const slot = var->index() + 1;
+    int const slot = var->index();
     int const depth = scope()->ContextChainLength(var->scope());
     if (depth <= StoreGlobalViaContextStub::kMaximumDepth) {
       __ Mov(StoreGlobalViaContextDescriptor::SlotRegister(), slot);