Add a generated ComputedStyleBase class that ComputedStyle extends

third_party/WebKit/Source/core/BUILD.gn

Index: third_party/WebKit/Source/core/BUILD.gn
diff --git a/third_party/WebKit/Source/core/BUILD.gn b/third_party/WebKit/Source/core/BUILD.gn
index 56c70401dd07081acf29f0bd3f6a502ed03ff669..988e6e2fb3f6cd1729f1220f1f86e7505efbcbc0 100644
--- a/third_party/WebKit/Source/core/BUILD.gn
+++ b/third_party/WebKit/Source/core/BUILD.gn
@@ -368,6 +368,20 @@ action("generated_testing_idls_internal_runtime_flags") {
   ]
 }
 
+css_properties("make_core_generated_computed_style_base") {
+  script = "../build/scripts/make_computed_style_base.py"
+  other_inputs = [
+    "../build/scripts/templates/ComputedStyleBase.cpp.tmpl",
+    "../build/scripts/templates/ComputedStyleBase.h.tmpl",
+    "../build/scripts/templates/ComputedStyleBaseConstants.h.tmpl",
+  ]
+  outputs = [
+    "$blink_core_output_dir/ComputedStyleBase.cpp",
+    "$blink_core_output_dir/ComputedStyleBase.h",
+    "$blink_core_output_dir/ComputedStyleBaseConstants.h",
+  ]
+}
+
 css_properties("make_core_generated_css_property_names") {
   script = "../build/scripts/make_css_property_names.py"
   outputs = [
@@ -809,6 +823,7 @@ target(core_link_small_target_type, "core_generated") {
     ":make_core_generated_bison",
     ":make_core_generated_css_primitive_value_unit_trie",
     ":make_core_generated_css_property_metadata",
+    ":make_core_generated_computed_style_base",
     ":make_core_generated_css_property_names",
     ":make_core_generated_cssom_types",
     ":make_core_generated_event_factory",