Fix RGBA alpha parsing and serialization to adhere to W3 standard.

third_party/WebKit/Source/core/css/parser/CSSParserFastPaths.cpp

Index: third_party/WebKit/Source/core/css/parser/CSSParserFastPaths.cpp
diff --git a/third_party/WebKit/Source/core/css/parser/CSSParserFastPaths.cpp b/third_party/WebKit/Source/core/css/parser/CSSParserFastPaths.cpp
index 19b0fb25922f37537ab040c552e34104e09ee99a..cb7a648492151faa5ab910cee63607b39a08616f 100644
--- a/third_party/WebKit/Source/core/css/parser/CSSParserFastPaths.cpp
+++ b/third_party/WebKit/Source/core/css/parser/CSSParserFastPaths.cpp
@@ -365,8 +365,10 @@ static inline bool parseAlphaValue(const CharacterType*& string,
   }
 
   if (isTenthAlpha(string, length - 1)) {
-    static const int tenthAlphaValues[] = {0,   25,  51,  76,  102,
-                                           127, 153, 179, 204, 230};
+    // Fast conversions for 0.1 steps of alpha values between 0.0 and 0.9,
+    // where 0.1 alpha is value 26 (25.5 rounded) and so on.
+    static const int tenthAlphaValues[] = {0,   26,  51,  77,  102,
+                                           128, 153, 179, 204, 230};
     value = negative ? 0 : tenthAlphaValues[string[length - 2] - '0'];
     string = end;
     return true;
@@ -375,9 +377,8 @@ static inline bool parseAlphaValue(const CharacterType*& string,
   double alpha = 0;
   if (!parseDouble(string, end, terminator, alpha))
     return false;
-  value = negative
-              ? 0
-              : static_cast<int>(std::min(alpha, 1.0) * nextafter(256.0, 0.0));
+  value =
+      negative ? 0 : static_cast<int>(roundf(std::min(alpha, 1.0) * 255.0f));
   string = end;
   return true;
 }