Update accept-language doc

No change to logic, this only updates a method doc to reflect the
method's current behavior.

GenerateAcceptLanguageHeader() decrements q-values by 0.1, not 0.2. I'm
not sure when the behavior changed. I observed this when using the
method (http://crrev.com/c/1637451), but this does not depend on nor
block that change.

Test: N/A
Change-Id: Ib45bd6f6da66ad80a6c675898000f71e165dbe13
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1637600Reviewed-by: Maks Orlovich <morlovich@chromium.org>
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#664921}

net/http/http_util.h

@@ -198,9 +198,9 @@ class NET_EXPORT HttpUtil {
   // Given a comma separated ordered list of language codes, return
   // the list with a qvalue appended to each language.
   // The way qvalues are assigned is rather simple. The qvalue
-  // starts with 1.0 and is decremented by 0.2 for each successive entry
-  // in the list until it reaches 0.2. All the entries after that are
-  // assigned the same qvalue of 0.2. Also, note that the 1st language
+  // starts with 1.0 and is decremented by 0.1 for each successive entry
+  // in the list until it reaches 0.1. All the entries after that are
+  // assigned the same qvalue of 0.1. Also, note that the 1st language
   // will not have a qvalue added because the absence of a qvalue implicitly
   // means q=1.0.
   //