Rework compositor touch hit testing

LayoutTests/fast/events/touch/resources/compositor-touch-hit-rects.css

+html[dumpRenderTree] {
+  font-family: Ahem;
+}
+#tests {
+ font-size: 10px;
+ width: 300px;
+}
+#tests > div {
+  margin: 5px;
+}
+.testcase:not(.generated), .testcase *:not(.generated) {
+  border: 1px solid red;
+}
+/* For manually visualizing how elements respond to hit-testing */
+.testcase:not(.generated):active, .testcase *:not(.generated):active {
+  background-color: yellow;
+}
+.overlay-container {
+  position: relative;
+  height: 0;
+  width: 0;
+  z-index: 10;
+}
+.overlay {
+  background-color: green;
+  opacity: 0.3;
+  pointer-events: none;
+  z-index: 10;
+}
+/* Don't show the overlays until we're all done testing, as they
+   can interfere with promotion to composited layers
+*/
+html:not([done]) .display-when-done {
+  display: none;
+}
+