[ignition] Avoid unnecessary ToName calls in VisitClassLiteralProperties

R=rmcilroy@chromium.org
BUG=v8:5799

Review-Url: https://codereview.chromium.org/2612903002
Cr-Commit-Position: refs/heads/master@{#42098}

src/interpreter/bytecode-generator.cc

@@ -1470,8 +1470,12 @@ void BytecodeGenerator::VisitClassLiteralProperties(ClassLiteral* expr,
       old_receiver = new_receiver;
     }
 
-    VisitForAccumulatorValue(property->key());
-    builder()->ConvertAccumulatorToName(key);
+    if (property->key()->IsStringLiteral()) {
+      VisitForRegisterValue(property->key(), key);
+    } else {
+      VisitForAccumulatorValue(property->key());
+      builder()->ConvertAccumulatorToName(key);
+    }
 
     if (property->is_static() && property->is_computed_name()) {
       // The static prototype property is read only. We handle the non computed

test/cctest/interpreter/bytecode_expectations/ClassDeclarations.golden

@@ -33,7 +33,7 @@ bytecodes: [
                 B(CallRuntime), U16(Runtime::kDefineClass), R(4), U8(4),
                 B(Star), R(4),
                 B(LdaConstant), U8(1),
-                B(ToName), R(6),
+                B(Star), R(6),
                 B(CreateClosure), U8(2), U8(2),
                 B(Star), R(7),
                 B(LdaSmi), U8(2),
@@ -84,7 +84,7 @@ bytecodes: [
                 B(CallRuntime), U16(Runtime::kDefineClass), R(4), U8(4),
                 B(Star), R(4),
                 B(LdaConstant), U8(1),
-                B(ToName), R(6),
+                B(Star), R(6),
                 B(CreateClosure), U8(2), U8(2),
                 B(Star), R(7),
                 B(LdaSmi), U8(2),
@@ -263,7 +263,7 @@ bytecodes: [
                 B(CallRuntime), U16(Runtime::kDefineClass), R(5), U8(4),
                 B(Star), R(5),
                 B(LdaConstant), U8(2),
-                B(ToName), R(7),
+                B(Star), R(7),
                 B(CreateClosure), U8(3), U8(2),
                 B(Star), R(8),
                 B(LdaSmi), U8(2),