[css-grid] Add use counter for percentage rows and indefinite height

CSSWG resolved back in January 2017 about how percentage rows
in a grid container with indefinite height work, to make them symmetric
to what happens for columns. Which has been ratified in the last
F2F meeting at TPAC 2017.
All this has been discussed in the following issue:
https://github.com/w3c/csswg-drafts/issues/1921

No browser is doing that right now, so it'd be nice to gather some data
about the usage of this before changing the implementation.
For that reason this patch adds a new use counter to check
when this change will have impact on real websites.

Change-Id: I61b82957d2bfe53912fd3e53a6bd41a6491a67be
Reviewed-on: https://chromium-review.googlesource.com/796855Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
Commit-Queue: Manuel Rego Casasnovas <rego@igalia.com>
Cr-Commit-Position: refs/heads/master@{#520213}

third_party/WebKit/Source/core/layout/GridTrackSizingAlgorithm.cpp

@@ -4,6 +4,7 @@
 
 #include "core/layout/GridTrackSizingAlgorithm.h"
 
+#include "core/frame/UseCounter.h"
 #include "core/layout/Grid.h"
 #include "core/layout/GridLayoutUtils.h"
 #include "core/layout/LayoutGrid.h"
@@ -739,6 +740,14 @@ void GridTrackSizingAlgorithm::InitializeTrackSizes() {
       flexible_sized_tracks_index_.push_back(i);
     if (track_size.HasAutoMaxTrackBreadth() && !track_size.IsFitContent())
       auto_sized_tracks_for_stretch_index_.push_back(i);
+
+    if (direction_ == kForRows &&
+        !layout_grid_->CachedHasDefiniteLogicalHeight() &&
+        (track_size.MinTrackBreadth().HasPercentage() ||
+         track_size.MaxTrackBreadth().HasPercentage())) {
+      UseCounter::Count(layout_grid_->GetDocument(),
+                        WebFeature::kGridRowTrackPercentIndefiniteHeight);
+    }
   }
 }
 

third_party/WebKit/public/platform/web_feature.mojom

@@ -1766,6 +1766,7 @@ enum WebFeature {
   kHTMLAnchorElementDownloadInSandboxWithUserGesture = 2245,
   kHTMLAnchorElementDownloadInSandboxWithoutUserGesture = 2246,
   kWindowOpenRealmMismatch = 2247,
+  kGridRowTrackPercentIndefiniteHeight = 2248,
 
   // Add new features immediately above this line. Don't change assigned
   // numbers of any item, and don't reuse removed slots.

tools/metrics/histograms/enums.xml

@@ -17059,6 +17059,7 @@ Called by update_net_error_codes.py.-->
   <int value="2246"
       label="HTMLAnchorElementDownloadInSandboxWithoutUserGesture"/>
   <int value="2247" label="WindowOpenRealmMismatch"/>
+  <int value="2248" label="GridRowTrackPercentIndefiniteHeight"/>
 </enum>
 
 <enum name="FeedbackSource">