scroll element into view for mouse actions

This works fine with Firefox, and conforms to the spec.

However, Chromium gets confused and clicks on the wrong position. Work
around that for now by keeping our old `ph_mouse()` event synthesizer
for Chromium.

test-functions.js

@@ -73,3 +73,59 @@ window.ph_wait_cond = function (cond, timeout, error_description) {
         step();
     });
 };
+
+// we only need this for Chromium, which mis-handles pointerMove with frames
+window.ph_mouse = function(sel, type, x, y, btn, ctrlKey, shiftKey, altKey, metaKey) {
+    const el = window.ph_find(sel);
+
+    /* The element has to be visible, and not collapsed */
+    if (el.offsetWidth <= 0 && el.offsetHeight <= 0 && el.tagName !== 'svg')
+        throw new Error(sel + " is not visible");
+
+    /* The event has to actually work */
+    let processed = false;
+    function handler() {
+        processed = true;
+    }
+
+    el.addEventListener(type, handler, true);
+
+    let elp = el;
+    let left = elp.offsetLeft || 0;
+    let top = elp.offsetTop || 0;
+    while (elp.offsetParent) {
+        elp = elp.offsetParent;
+        left += elp.offsetLeft;
+        top += elp.offsetTop;
+    }
+
+    let detail = 0;
+    if (["click", "mousedown", "mouseup"].indexOf(type) > -1)
+        detail = 1;
+    else if (type === "dblclick")
+        detail = 2;
+
+    const ev = new MouseEvent(type, {
+        bubbles: true,
+        cancelable: true,
+        view: window,
+        detail,
+        screenX: left + x,
+        screenY: top + y,
+        clientX: left + x,
+        clientY: top + y,
+        button: btn,
+        ctrlKey: ctrlKey || false,
+        shiftKey: shiftKey || false,
+        altKey: altKey || false,
+        metaKey: metaKey || false
+    });
+
+    el.dispatchEvent(ev);
+
+    el.removeEventListener(type, handler, true);
+
+    /* It really had to work */
+    if (!processed)
+        throw new Error(sel + " is disabled or somehow doesn't process events");
+};