Update FeatureObserver histograms.xml definition.

Generated using
src/tools/metrics/histograms/update_use_counter_feature_enum.py

Corresponding Blink changes:
https://codereview.chromium.org/337283003 (by mahesh.kk@sumsung.com)
https://codereview.chromium.org/339563004 (by me)

NOTRY=true
BUG=383749

Review URL: https://codereview.chromium.org/342113003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@278624 0039d316-1c4b-4281-b951-d872f2087c98

tools/metrics/histograms/histograms.xml

@@ -37401,6 +37401,13 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="462" label="EditingAppleTabSpanClass"/>
   <int value="463" label="HTMLImportsAsyncAttribute"/>
   <int value="464" label="FontFaceSetReady"/>
+  <int value="465" label="XMLHttpRequestSynchronous"/>
+  <int value="466" label="CSSSelectorPseudoUnresolved"/>
+  <int value="467" label="CSSSelectorPseudoShadow"/>
+  <int value="468" label="CSSSelectorPseudoContent"/>
+  <int value="469" label="CSSSelectorPseudoHost"/>
+  <int value="470" label="CSSSelectorPseudoHostContext"/>
+  <int value="471" label="CSSDeepCombinator"/>
 </enum>
 
 <enum name="FFmpegCodecs" type="int">