Add most missing blink files to .gn files

third_party/WebKit/Source/core/css/BUILD.gn

Index: third_party/WebKit/Source/core/css/BUILD.gn
diff --git a/third_party/WebKit/Source/core/css/BUILD.gn b/third_party/WebKit/Source/core/css/BUILD.gn
index cbb07da89ea170b7f3ca7a2265188df4130e0988..ed9389d2e12b79e808a2702ca8b190a607a08f7b 100644
--- a/third_party/WebKit/Source/core/css/BUILD.gn
+++ b/third_party/WebKit/Source/core/css/BUILD.gn
@@ -73,6 +73,7 @@ blink_core_sources("css") {
     "CSSGridTemplateAreasValue.h",
     "CSSGroupingRule.cpp",
     "CSSGroupingRule.h",
+    "CSSHelper.h",
     "CSSIdentifierValue.cpp",
     "CSSIdentifierValue.h",
     "CSSImageGeneratorValue.cpp",
@@ -116,12 +117,14 @@ blink_core_sources("css") {
     "CSSProperty.h",
     "CSSPropertyEquality.cpp",
     "CSSPropertyEquality.h",
+    "CSSPropertyIDTemplates.h",
     "CSSPropertySourceData.cpp",
     "CSSPropertySourceData.h",
     "CSSQuadValue.cpp",
     "CSSQuadValue.h",
     "CSSReflectValue.cpp",
     "CSSReflectValue.h",
+    "CSSReflectionDirection.h",
     "CSSRule.cpp",
     "CSSRule.h",
     "CSSRuleList.cpp",
@@ -338,9 +341,11 @@ blink_core_sources("css") {
     "parser/CSSParserContext.h",
     "parser/CSSParserFastPaths.cpp",
     "parser/CSSParserFastPaths.h",
+    "parser/CSSParserIdioms.h",
     "parser/CSSParserImpl.cpp",
     "parser/CSSParserImpl.h",
     "parser/CSSParserMode.h",
+    "parser/CSSParserObserver.h",
     "parser/CSSParserObserverWrapper.cpp",
     "parser/CSSParserObserverWrapper.h",
     "parser/CSSParserSelector.cpp",
@@ -492,10 +497,12 @@ blink_core_sources("css") {
     "properties/CSSPropertyLengthUtils.h",
     "properties/CSSPropertyMarginUtils.cpp",
     "properties/CSSPropertyMarginUtils.h",
+    "properties/CSSPropertyPositionUtils.h",
     "properties/CSSPropertyShapeUtils.cpp",
     "properties/CSSPropertyShapeUtils.h",
     "resolver/AnimatedStyleBuilder.cpp",
     "resolver/AnimatedStyleBuilder.h",
+    "resolver/CSSPropertyPriority.h",
     "resolver/CSSToStyleMap.cpp",
     "resolver/CSSToStyleMap.h",
     "resolver/CSSVariableResolver.cpp",