[Bindings] Emit less code per member in generated dictionary ToV8.

third_party/WebKit/Source/bindings/templates/dictionary_v8.cpp.tmpl

 {% filter format_blink_cpp_source_code %}
 
 {% from 'utilities.cpp.tmpl' import declare_enum_validation_variable %}
 {% include 'copyright_block.txt' %}
 #include "{{v8_original_class}}.h"
 
 {% for filename in cpp_includes if filename != '%s.h' % v8_class %}
 #include "{{filename}}"
 {% endfor %}
 
@@ skipping 82 matching lines @@
   return v8Object;
 }
 
 bool toV8{{cpp_class}}(const {{cpp_class}}& impl, v8::Local<v8::Object> dictionary, v8::Local<v8::Object> creationContext, v8::Isolate* isolate) {
   {% if parent_v8_class %}
   if (!toV8{{parent_cpp_class}}(impl, dictionary, creationContext, isolate))
     return false;
 
   {% endif %}
   {% for member in members %}
+  v8::Local<v8::Value> {{member.name}}Value;
+  bool {{member.name}}HasValueOrDefault = false;
   if (impl.{{member.has_method_name}}()) {
     {% if member.is_object %}
     DCHECK(impl.{{member.getter_name}}().isObject());
     {% endif %}
-    if (!v8CallBoolean(dictionary->CreateDataProperty(isolate->GetCurrentContext(), v8AtomicString(isolate, "{{member.name}}"), {{member.cpp_value_to_v8_value}})))
-      return false;
+    {{member.name}}Value = {{member.cpp_value_to_v8_value}};
+    {{member.name}}HasValueOrDefault = true;
   {% if member.v8_default_value %}
   } else {
-    if (!v8CallBoolean(dictionary->CreateDataProperty(isolate->GetCurrentContext(), v8AtomicString(isolate, "{{member.name}}"), {{member.v8_default_value}})))
-      return false;
+    {{member.name}}Value = {{member.v8_default_value}};
+    {{member.name}}HasValueOrDefault = true;
   {% elif member.is_nullable %}
   } else {
-    if (!v8CallBoolean(dictionary->CreateDataProperty(isolate->GetCurrentContext(), v8AtomicString(isolate, "{{member.name}}"), v8::Null(isolate))))
-      return false;
+    {{member.name}}Value = v8::Null(isolate);
+    {{member.name}}HasValueOrDefault = true;
   {% elif member.is_required %}
   } else {
     NOTREACHED();
   {% endif %}
   }
+  {# The HasValueOrDefault variable will be optimized out.
+     If there is a default value, the compiler will notice that all branches set it to true.
+     If there is not, then the compiler will inline this call into the only branch that sets it to true.
+     Either way, the code is efficient and the variable is completely elided. #}
+  if ({{member.name}}HasValueOrDefault &&
+      !v8CallBoolean(dictionary->CreateDataProperty(isolate->GetCurrentContext(), v8AtomicString(isolate, "{{member.name}}"), {{member.name}}Value))) {
+    return false;
+  }
 
   {% endfor %}
   return true;
 }
 
 {{cpp_class}} NativeValueTraits<{{cpp_class}}>::nativeValue(v8::Isolate* isolate, v8::Local<v8::Value> value, ExceptionState& exceptionState) {
   {{cpp_class}} impl;
   {{v8_class}}::toImpl(isolate, value, impl, exceptionState);
   return impl;
 }
 
 }  // namespace blink
 
 {% endfilter %}{# format_blink_cpp_source_code #}