[Typed OM] Add an "UnsupportedStyleValue" in C++ that just has a string for unknown types

third_party/WebKit/Source/core/core.gypi

 {
     'includes': [
         'core_generated.gypi',
     ],
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/KeyframeEffect.idl',
             'animation/EffectModel.idl',
             'animation/AnimationEffectReadOnly.idl',
@@ skipping 1342 matching lines @@
             'css/cssom/CSSRotation.cpp',
             'css/cssom/CSSRotation.h',
             'css/cssom/CSSScale.cpp',
             'css/cssom/CSSScale.h',
             'css/cssom/CSSSimpleLength.cpp',
             'css/cssom/CSSSimpleLength.h',
             'css/cssom/CSSSkew.cpp',
             'css/cssom/CSSSkew.h',
             'css/cssom/CSSStyleValue.cpp',
             'css/cssom/CSSStyleValue.h',
+            'css/cssom/CSSUnsupportedStyleValue.cpp',
+            'css/cssom/CSSUnsupportedStyleValue.h',
             'css/cssom/CSSTranslation.cpp',
             'css/cssom/CSSTranslation.h',
             'css/cssom/ComputedStylePropertyMap.cpp',
             'css/cssom/ComputedStylePropertyMap.h',
             'css/cssom/ImmutableStylePropertyMap.h',
             'css/cssom/InlineStylePropertyMap.cpp',
             'css/cssom/InlineStylePropertyMap.h',
             'css/cssom/MutableStylePropertyMap.h',
             'css/cssom/StylePropertyMap.cpp',
             'css/cssom/StylePropertyMap.h',
@@ skipping 2798 matching lines @@
             'testing/PrivateScriptTestTest.cpp',
             'timing/MemoryInfoTest.cpp',
             'timing/PerformanceBaseTest.cpp',
             'timing/PerformanceObserverTest.cpp',
             'workers/WorkerThreadTest.cpp',
             'workers/WorkerThreadTestHelper.h',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }