Remove MainThreadScrollingReasons::kHasClipRelatedProperty

We no longer need to skip composited scrolling for css clip and
clip-path since (perhaps) BlinkGenPropertyTrees.

In compositor, when we hit test on a layer with special clip/mask,
we'll still fallback to main thread hit testing/scrolling because only
the main thread knows which area is hit testable. This is achieved by
cc::LayerTreeHostImpl::IsInitialScrollHitTestReliable() returning false.

Bug: 1074395
Change-Id: I91260b063879812ca82928fe783de25c4b6732a3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2225229
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774232}
diff --git a/css/css-masking/clip-path/clip-path-scroll.html b/css/css-masking/clip-path/clip-path-scroll.html
new file mode 100644
index 0000000..880fd8b
--- /dev/null
+++ b/css/css-masking/clip-path/clip-path-scroll.html
@@ -0,0 +1,24 @@
+<!DOCTYPE html>
+<title>CSS Masking: Test clip-path property with overflow:scroll</title>
+<link rel="help" href="http://www.w3.org/TR/css-masking-1/#clip-path-property">
+<link rel="match" href="reference/clip-path-scroll-ref.html">
+<html class="reftest-wait">
+<p>The test passes if there is a green square containing text (which can be scrolled
+with mouse wheel or touch). No scrollbars should be seen.</p>
+<div id="target" style="clip-path: polygon(10px 10px, 10px 100px, 100px 100px, 100px 10px);
+            width: 200px; height: 200px; overflow: scroll; background: red">
+  <div style="position: relative; top: 100px;
+              width: 100px; height: 100px; background: green">
+  </div>
+  <div style="height: 1000px"></div>
+</div>
+<script>
+requestAnimationFrame(() => {
+  requestAnimationFrame(() => {
+    target.scrollTop = 100;
+    document.documentElement.classList.remove("reftest-wait");
+  });
+});
+</script>
+</html>
+
diff --git a/css/css-masking/clip-path/reference/clip-path-scroll-ref.html b/css/css-masking/clip-path/reference/clip-path-scroll-ref.html
new file mode 100644
index 0000000..a647e8a
--- /dev/null
+++ b/css/css-masking/clip-path/reference/clip-path-scroll-ref.html
@@ -0,0 +1,5 @@
+<!DOCTYPE html>
+<p>The test passes if there is a green square containing text (which can be scrolled
+with mouse wheel or touch). No scrollbars should be seen.</p>
+<div style="position: relative; top: 10px; left: 10px; width: 90px; height: 90px; background: green">
+</div>
diff --git a/css/css-masking/clip/clip-rect-scroll.html b/css/css-masking/clip/clip-rect-scroll.html
new file mode 100644
index 0000000..0c84ee2
--- /dev/null
+++ b/css/css-masking/clip/clip-rect-scroll.html
@@ -0,0 +1,24 @@
+<!DOCTYPE html>
+<title>CSS Masking: Test clip property with rect function with overflow:scroll</title>
+<link rel="help" href="http://www.w3.org/TR/css-masking-1/#clip-property">
+<link rel="match" href="reference/clip-rect-scroll-ref.html">
+<html class="reftest-wait">
+<p>The test passes if there is a green square containing text (which can be scrolled
+with mouse wheel or touch). No scrollbars should be seen.</p>
+<div id="target" style="position: absolute; clip: rect(10px,100px,100px,10px);
+            width: 200px; height: 200px; overflow: scroll; background: red">
+  <div style="position: relative; top: 100px;
+              width: 100px; height: 100px; background: green">
+  </div>
+  <div style="height: 1000px"></div>
+</div>
+<script>
+requestAnimationFrame(() => {
+  requestAnimationFrame(() => {
+    target.scrollTop = 100;
+    document.documentElement.classList.remove("reftest-wait");
+  });
+});
+</script>
+</html>
+
diff --git a/css/css-masking/clip/reference/clip-rect-scroll-ref.html b/css/css-masking/clip/reference/clip-rect-scroll-ref.html
new file mode 100644
index 0000000..a647e8a
--- /dev/null
+++ b/css/css-masking/clip/reference/clip-rect-scroll-ref.html
@@ -0,0 +1,5 @@
+<!DOCTYPE html>
+<p>The test passes if there is a green square containing text (which can be scrolled
+with mouse wheel or touch). No scrollbars should be seen.</p>
+<div style="position: relative; top: 10px; left: 10px; width: 90px; height: 90px; background: green">
+</div>