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

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

Index: third_party/WebKit/Source/core/css/parser/CSSPropertyParserHelpers.cpp
diff --git a/third_party/WebKit/Source/core/css/parser/CSSPropertyParserHelpers.cpp b/third_party/WebKit/Source/core/css/parser/CSSPropertyParserHelpers.cpp
index c4c2011d5f00436317e2473f73d26fc4870847dd..b356ef92c62f51e7d8094b62005ac515544848ad 100644
--- a/third_party/WebKit/Source/core/css/parser/CSSPropertyParserHelpers.cpp
+++ b/third_party/WebKit/Source/core/css/parser/CSSPropertyParserHelpers.cpp
@@ -433,10 +433,9 @@ static bool parseRGBParameters(CSSParserTokenRange& range,
     double alpha;
     if (!consumeNumberRaw(args, alpha))
       return false;
-    // Convert the floating pointer number of alpha to an integer in the range
-    // [0, 256), with an equal distribution across all 256 values.
-    int alphaComponent = static_cast<int>(clampTo<double>(alpha, 0.0, 1.0) *
-                                          nextafter(256.0, 0.0));
+    // W3 standard stipulates a 2.55 alpha value multiplication factor.
+    int alphaComponent =
+        static_cast<int>(lroundf(clampTo<double>(alpha, 0.0, 1.0) * 255.0f));
     result =
         makeRGBA(colorArray[0], colorArray[1], colorArray[2], alphaComponent);
   } else {