Style: Allow multiple aliases of a single CSS property in css_properties.json5

make_css_property_names.py supports multiple aliases.
Before this CL, |<a resolved property id> + 1024| was an an alias.
Since this CL, |<a resolved property id> + 1024 * n| is an alias where
|n| is a natural number.

This CL will be necessary for unprefixing -webkit-text-emphasis, which
already has -epub-text-emphasis alias.

This CL has no behavior changes for now.

Bug: 666433
Change-Id: I6e620b55f07fde7542d1bd04fa25beaad8ee659e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2596466Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#838403}

third_party/blink/renderer/build/scripts/core/css/css_properties.py

@@ -67,6 +67,7 @@ class CSSProperties(object):
         # in the various generators for ComputedStyle.
         self._field_alias_expander = FieldAliasExpander(file_paths[1])
 
+        # _alias_offset must be a power of 2.
         self._alias_offset = 1024
         # 0: CSSPropertyID::kInvalid
         # 1: CSSPropertyID::kVariable
@@ -224,7 +225,7 @@ class CSSProperties(object):
             updated_alias['enum_key'] = enum_key_for_css_property_alias(
                 alias['name'])
             updated_alias['enum_value'] = aliased_property['enum_value'] + \
-                self._alias_offset
+                self._alias_offset * len(aliased_property['aliases'])
             updated_alias['superclass'] = 'CSSUnresolvedProperty'
             updated_alias['namespace_group'] = \
                 'Shorthand' if aliased_property['longhands'] else 'Longhand'

third_party/blink/renderer/build/scripts/core/css/make_css_property_names.py

@@ -29,8 +29,8 @@ class CSSPropertyNamesWriter(json5_generator.Writer):
         'core/css/templates/css_property_names.h.tmpl')
     def generate_header(self):
         return {
-            'alias_offset':
-            self._css_properties.alias_offset,
+            'alias_mask':
+            hex(0xffffffff - self._css_properties.alias_offset + 1),
             'class_name':
             self.class_name,
             'property_enums':

third_party/blink/renderer/build/scripts/core/css/templates/css_property_names.h.tmpl

@@ -83,10 +83,10 @@ inline CSSPropertyID convertToCSSPropertyID(int value)
 
 inline CSSPropertyID resolveCSSPropertyID(CSSPropertyID id)
 {
-    return convertToCSSPropertyID(static_cast<int>(id) & ~{{alias_offset}});
+    return convertToCSSPropertyID(static_cast<int>(id) & ~{{alias_mask}});
 }
 
-inline bool isPropertyAlias(CSSPropertyID id) { return static_cast<int>(id) & {{alias_offset}}; }
+inline bool isPropertyAlias(CSSPropertyID id) { return static_cast<int>(id) & {{alias_mask}}; }
 
 CSSPropertyID CORE_EXPORT unresolvedCSSPropertyID(const ExecutionContext*, const WTF::String&);