Add use counter for cursor with prefixed grab and grabbing value

unprefixed versions of the "grab" and "grabbing" CSS cursors
were not supported at blink.
so we should check how many use prefixed values before retire
that values. and i will make another patch to support
unprefixed values parallelly.

Bug: 708197
Change-Id: Ic882d9d6d5bc18724f3802c8ab2336668074f17d
Reviewed-on: https://chromium-review.googlesource.com/1011883
Commit-Queue: Eric Willigers <ericwilligers@chromium.org>
Reviewed-by: Eric Willigers <ericwilligers@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550549}

third_party/blink/public/platform/web_feature.mojom

@@ -1908,6 +1908,8 @@ enum WebFeature {
   kXRSupportsSession = 2416,
   kXRSessionGetInputSources = 2417,
   kCSSResizeAuto = 2418,
+  kPrefixedCursorGrab = 2419,
+  kPrefixedCursorGrabbing = 2420,
 
   // Add new features immediately above this line. Don't change assigned
   // numbers of any item, and don't reuse removed slots.

third_party/blink/renderer/core/css/properties/longhands/cursor_custom.cc

@@ -49,6 +49,10 @@ const CSSValue* Cursor::ParseSingleValue(CSSParserTokenRange& range,
       context.Count(WebFeature::kPrefixedCursorZoomIn);
     else if (id == CSSValueWebkitZoomOut)
       context.Count(WebFeature::kPrefixedCursorZoomOut);
+    else if (id == CSSValueWebkitGrab)
+      context.Count(WebFeature::kPrefixedCursorGrab);
+    else if (id == CSSValueWebkitGrabbing)
+      context.Count(WebFeature::kPrefixedCursorGrabbing);
   }
   CSSValue* cursor_type = nullptr;
   if (id == CSSValueHand) {

tools/metrics/histograms/enums.xml

@@ -18280,6 +18280,8 @@ Called by update_net_error_codes.py.-->
   <int value="2416" label="XRSupportsSession"/>
   <int value="2417" label="XRSessionGetInputSources"/>
   <int value="2418" label="CSSResizeAuto"/>
+  <int value="2419" label="PrefixedCursorGrab"/>
+  <int value="2420" label="PrefixedCursorGrabbing"/>
 </enum>
 
 <enum name="FeedbackSource">