This came up in a profile for bug 297959. The breakdown for time spent under nsCanvasRenderingContext2D::StyleVariantToColor is: 14334 CSSParserImpl::ParseColorString 3383 XPCVariant::GetAsWStringWithSize 2110 nsSubstring::Assign 978 nsAString_internal::~nsAString_internal() 406 NS_Free_P 358 nsVariant::ConvertToWStringWithSize and small fry. Note all the string-munging. What we're doing (when you look at the GetAsWStringWithSize method on variants) is: 1) Creating a dependent string inside the variant. 2) Doing ToNewUnicode on it. 3) Creating an nsString using the result in the caller I suggest that instead of calling GetAsWStringWithSize we should just call GetAsAString here and pass an nsAutoString. That will involve one single string copy (instead of the two we have here) and probably zero heap allocations (instead of the two we have here) because color strings are short.

Comment on attachment 198853 [details] [diff] [review] Like so r=vladimir

Comment on attachment 198853 [details] [diff] [review] Like so sr=darin Too bad we don't have a way to get a dependent string out of a variant.

Fixed on trunk