[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..348b26eb36233a518a1e77384b358418acf1dcf1 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,
+        'api_experiment_enabled': api_experiment_enabled_if,
         })
     return jinja_env
 
@@ -437,6 +438,16 @@ def runtime_enabled_if(code, runtime_enabled_function_name):
     return generate_indented_conditional(code, '%s()' % runtime_enabled_function_name)
 
 
+# [APIExperimentEnabled]
+def api_experiment_enabled_if(code, api_experiment_name, error_message=None):
+    if not api_experiment_name:
+        return code
+    if error_message:
+        conditional = 'Experiments::isApiEnabled(currentExecutionContext(isolate), "%s", %s)' % (api_experiment_name, error_message)
+    else:
+        conditional = 'Experiments::isApiEnabledWithoutMessage(currentExecutionContext(isolate), "%s")' % api_experiment_name
+    return generate_indented_conditional(code, conditional)
+
 ################################################################################
 
 def main(argv):