Fixed a variable that may be used uninitialized.

Source/core/css/parser/BisonCSSParser-in.cpp

Index: Source/core/css/parser/BisonCSSParser-in.cpp
diff --git a/Source/core/css/parser/BisonCSSParser-in.cpp b/Source/core/css/parser/BisonCSSParser-in.cpp
index 1bd084d72375943a7a35fee7d38c69982bc969b6..de46fa0aba793e4e4383eef4d0d8a9750c9bcfc4 100644
--- a/Source/core/css/parser/BisonCSSParser-in.cpp
+++ b/Source/core/css/parser/BisonCSSParser-in.cpp
@@ -331,7 +331,7 @@ static inline bool parseSimpleLength(const CharacterType* characters, unsigned l
 static bool parseSimpleLengthValue(MutableStylePropertySet* declaration, CSSPropertyID propertyId, const String& string, bool important, CSSParserMode cssParserMode)
 {
     ASSERT(!string.isEmpty());
-    bool acceptsNegativeNumbers;
+    bool acceptsNegativeNumbers = false;
 
     // In @viewport, width and height are shorthands, not simple length values.
     if (isCSSViewportParsingEnabledForMode(cssParserMode) || !isSimpleLengthPropertyID(propertyId, acceptsNegativeNumbers))