[bindings] Implement an ExperimentEnabled IDL extended attribute.

third_party/WebKit/Source/bindings/templates/attributes.cpp

Index: third_party/WebKit/Source/bindings/templates/attributes.cpp
diff --git a/third_party/WebKit/Source/bindings/templates/attributes.cpp b/third_party/WebKit/Source/bindings/templates/attributes.cpp
index 89604a191368913c98024872a6205b5d2d9ea3b4..d36c5b5060170c129167f92fc4e43458365ee19b 100644
--- a/third_party/WebKit/Source/bindings/templates/attributes.cpp
+++ b/third_party/WebKit/Source/bindings/templates/attributes.cpp
@@ -11,6 +11,13 @@ const v8::PropertyCallbackInfo<v8::Value>& info
 const v8::FunctionCallbackInfo<v8::Value>& info
 {%- endif %})
 {
+    {% if attribute.experimental_api_name %}
+    String errorMessage;

[haraken, 2015/12/16 02:16:41]

What is this errorMessage for?

[Daniel Nishi, 2015/12/16 21:42:02]

It explains why an experiment may have failed.

When the error is unnecessary, I've changed the patch to not take a useless
error string.

+    if (!Experiments::isApiEnabled(currentExecutionContext(info.GetIsolate()), "{{ attribute.experimental_api_name }}", errorMessage)) {

[haraken, 2015/12/16 02:16:41]

Do you have a CL to implement the isAPIEnabled?

I'm fine with landing this CL without Experiments.h but want to see how it
looks.

[Daniel Nishi, 2015/12/16 21:42:02]

https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

+        v8SetReturnValue(info, v8::Undefined(info.GetIsolate()));
+        return;
+    }
+    {% endif %}
     {% if attribute.is_reflect and not attribute.is_url
           and attribute.idl_type == 'DOMString' and is_node
           and not attribute.is_implemented_in_private_script %}
@@ -468,7 +475,7 @@ bool {{v8_class}}::PrivateScript::{{attribute.name}}AttributeSetter(LocalFrame*
 {% set getter_callback =
        '%sV8Internal::%sConstructorGetterCallback' % (cpp_class_or_partial, attribute.name)
        if attribute.needs_constructor_getter_callback else
-       'v8ConstructorAttributeGetter' %}
+       'is%sExperimentallyEnabled' % attribute.name if attribute.experimental_api_name else 'v8ConstructorAttributeGetter' %}

[haraken, 2015/12/16 02:16:41]

Avoid using "if ... else ... if ... else".

[Daniel Nishi, 2015/12/16 21:42:02]

I've removed this by eliminating is%sExperimentallyEnabled.

 {% set setter_callback =
        '%sV8Internal::%sAttributeSetterCallback' % (cpp_class_or_partial, attribute.name)
        if attribute.needs_constructor_setter_callback else