[bindings] Implement an ExperimentEnabled IDL extended attribute.

third_party/WebKit/Source/bindings/scripts/code_generator_v8.py

Index: third_party/WebKit/Source/bindings/scripts/code_generator_v8.py
diff --git a/third_party/WebKit/Source/bindings/scripts/code_generator_v8.py b/third_party/WebKit/Source/bindings/scripts/code_generator_v8.py
index 110e8e86368557bf0d9baeb3df52de50ff09503d..e28f6a8181f444749b97ad75275aa230deab9771 100644
--- a/third_party/WebKit/Source/bindings/scripts/code_generator_v8.py
+++ b/third_party/WebKit/Source/bindings/scripts/code_generator_v8.py
@@ -401,6 +401,7 @@ def initialize_jinja_env(cache_dir):
         'conditional': conditional_if_endif,
         'exposed': exposed_if,
         'runtime_enabled': runtime_enabled_if,
+        'experiment_enabled': experiment_enabled_if,
         })
     return jinja_env
 
@@ -437,6 +438,12 @@ def runtime_enabled_if(code, runtime_enabled_function_name):
     return generate_indented_conditional(code, '%s()' % runtime_enabled_function_name)
 
 
+# [ExperimentEnabled]
+def experiment_enabled_if(code, experiment_name, error_message):
+    if not experiment_name:
+        return code
+    return generate_indented_conditional(code, 'Experiments::isApiEnabled(currentExecutionContext(isolate), "%s", %s)' % (experiment_name, error_message))
+
 ################################################################################
 
 def main(argv):