Add IDL parsing of FeaturePolicy extended attribute

This is an interim step to handle FeaturePolicy-enabled features, before the
three conditional feature flags (RuntimeEnabled, OriginTrialEnabled and
FeaturePolicy) are eventually combined into a common 'Feature' attribute.

BUG=638240

Review-Url: https://codereview.chromium.org/2247923004
Cr-Commit-Position: refs/heads/master@{#412524}

third_party/WebKit/Source/bindings/IDLExtendedAttributes.txt

@@ -52,6 +52,7 @@ DoNotCheckSecurity=|Setter
 DoNotTestNewObject
 EnforceRange
 Exposed=*
+FeaturePolicy=*
 FlexibleArrayBufferView
 Global=|*
 ImplementedAs=*

third_party/WebKit/Source/bindings/scripts/v8_utilities.py

@@ -403,7 +403,7 @@ def origin_trial_enabled_function_name(definition_or_member):
     extended_attributes = definition_or_member.extended_attributes
     is_origin_trial_enabled = 'OriginTrialEnabled' in extended_attributes
 
-    if (is_origin_trial_enabled and 'RuntimeEnabled' in extended_attributes):
+    if is_origin_trial_enabled and 'RuntimeEnabled' in extended_attributes:
         raise Exception('[OriginTrialEnabled] and [RuntimeEnabled] must '
                         'not be specified on the same definition: '
                         '%s.%s' % (definition_or_member.idl_name, definition_or_member.name))
@@ -412,14 +412,26 @@ def origin_trial_enabled_function_name(definition_or_member):
         trial_name = extended_attributes['OriginTrialEnabled']
         return 'OriginTrials::%sEnabled' % uncapitalize(trial_name)
 
+    is_feature_policy_enabled = 'FeaturePolicy' in extended_attributes
+
+    if is_feature_policy_enabled and 'RuntimeEnabled' in extended_attributes:
+        raise Exception('[FeaturePolicy] and [RuntimeEnabled] must '
+                        'not be specified on the same definition: '
+                        '%s.%s' % (definition_or_member.idl_name, definition_or_member.name))
+
+    if is_feature_policy_enabled:
+        includes.add('bindings/core/v8/ScriptState.h')
+        includes.add('platform/feature_policy/FeaturePolicy.h')
+
+        trial_name = extended_attributes['FeaturePolicy']
+        return 'FeaturePolicy::%sEnabled' % uncapitalize(trial_name)
+
     return None
 
 
 def origin_trial_feature_name(definition_or_member):
     extended_attributes = definition_or_member.extended_attributes
-    if 'OriginTrialEnabled' not in extended_attributes:
-        return None
-    return extended_attributes['OriginTrialEnabled']
+    return extended_attributes.get('OriginTrialEnabled') or extended_attributes.get('FeaturePolicy')
 
 
 def runtime_feature_name(definition_or_member):

third_party/WebKit/Source/build/scripts/make_runtime_features.py

@@ -43,13 +43,14 @@ class RuntimeFeatureWriter(in_generator.Writer):
         'status': ['stable', 'experimental', 'test'],
     }
     defaults = {
-        'origin_trial_feature_name': None,
         'condition': None,
-        'implied_by': [],
-        'depends_on': [],
         'custom': False,
-        'status': None,
+        'depends_on': [],
+        'feature_policy': None,
+        'implied_by': [],
+        'origin_trial_feature_name': None,
         'settable_from_internals': False,
+        'status': None,
     }
 
     def __init__(self, in_file_path):