Separate CSSValueID mappings generator from ComputedStyleBase generator.

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 57f7da07547d86aa867e97d733b190a53f8a47e0..f09f49e0bbd4728427c5ee680f996d0c5d3f44ac 100644
--- a/third_party/WebKit/Source/core/BUILD.gn
+++ b/third_party/WebKit/Source/core/BUILD.gn
@@ -418,12 +418,19 @@ css_properties("make_core_generated_computed_style_base") {
     "../build/scripts/templates/ComputedStyleBase.cpp.tmpl",
     "../build/scripts/templates/ComputedStyleBase.h.tmpl",
     "../build/scripts/templates/ComputedStyleBaseConstants.h.tmpl",
-    "../build/scripts/templates/CSSValueIDMappingsGenerated.h.tmpl",
   ]
   outputs = [
     "$blink_core_output_dir/ComputedStyleBase.cpp",
     "$blink_core_output_dir/ComputedStyleBase.h",
     "$blink_core_output_dir/ComputedStyleBaseConstants.h",
+  ]
+}
+
+css_properties("make_core_generated_css_value_id_mappings") {
+  script = "../build/scripts/make_css_value_id_mappings.py"
+  other_inputs =
+      [ "../build/scripts/templates/CSSValueIDMappingsGenerated.h.tmpl" ]
+  outputs = [
     "$blink_core_output_dir/CSSValueIDMappingsGenerated.h",
   ]
 }
@@ -987,6 +994,7 @@ targets_generating_sources = [
   ":make_core_generated_css_primitive_value_unit_trie",
   ":make_core_generated_css_property_metadata",
   ":make_core_generated_computed_style_base",
+  ":make_core_generated_css_value_id_mappings",
   ":make_core_generated_css_property_apis",
   ":make_core_generated_css_property_names",
   ":make_core_generated_cssom_types",