Made CSSPrimitiveValue::getString() only work for String types

Source/core/css/resolver/StyleBuilderCustom.cpp

Index: Source/core/css/resolver/StyleBuilderCustom.cpp
diff --git a/Source/core/css/resolver/StyleBuilderCustom.cpp b/Source/core/css/resolver/StyleBuilderCustom.cpp
index b14daca0eb8dfc95bba91c99f72014d4cf8ad14f..635bef4464943c6f626419b8c9ffb6946a6e782e 100644
--- a/Source/core/css/resolver/StyleBuilderCustom.cpp
+++ b/Source/core/css/resolver/StyleBuilderCustom.cpp
@@ -769,10 +769,12 @@ void StyleBuilderFunctions::applyValueCSSPropertyContent(StyleResolverState& sta
 void StyleBuilderFunctions::applyValueCSSPropertyWebkitLocale(StyleResolverState& state, CSSValue* value)
 {
     const CSSPrimitiveValue* primitiveValue = toCSSPrimitiveValue(value);
-    if (primitiveValue->getValueID() == CSSValueAuto)
+    if (primitiveValue->getValueID() == CSSValueAuto) {
         state.style()->setLocale(nullAtom);
-    else
+    } else {
+        ASSERT(primitiveValue->isString());
         state.style()->setLocale(AtomicString(primitiveValue->getStringValue()));
+    }
     state.fontBuilder().setScript(state.style()->locale());
 }