Align drag feedback for links with draggable="true" to Safari.

third_party/WebKit/LayoutTests/fast/dnd/resources/link-dragging-common.js

+const mouseMoveToCenter = (element) => {
+  const clientRect = element.getBoundingClientRect();
+  const centerX = (clientRect.left + clientRect.right) / 2;
+  const centerY = (clientRect.top + clientRect.bottom) / 2;
+  eventSender.mouseMoveTo(centerX, centerY);
+}
+
+const runLinkDraggingTest = (t, params) => {
+  let gotDragStart = false
+  let dragStartEffect = null;
+  let dragStartUriList = null;
+  let dragStartTypes = null;
+  let dragSource = null;
+
+  // Enables the Ahem font, which makes the drag image platform-independent.
+  if (window.testRunner)
+    document.body.setAttribute('class', 'test-runner');
+
+  const dragged = document.querySelector('.dragged');
+  dragged.ondragstart = (event) => {
+    if (!gotDragStart) {
+      gotDragStart = true;
+      dragStartEffect = event.dataTransfer.dropEffect;
+      dragStartUriList = event.dataTransfer.getData('text/uri-list');
+      dragStartTypes = [].concat(event.dataTransfer.types).sort();
+      dragStartTarget = event.target;
+    }
+  }
+
+  let gotDrop = false;
+  let dropEffect = null;
+  const dropZone = document.querySelector('.dropzone');
+  dropZone.ondragover = (event) => event.preventDefault();
+
+  const testDone = document.querySelector('.done');
+  return new Promise((resolve, reject) => {
+    dropZone.ondrop = (event) => {
+      if (!gotDrop) {
+        gotDrop = true;
+        dropEffect = event.dataTransfer.dropEffect;
+      }
+      // Some of the drags would result in the link being followed in Firefox.
+      event.preventDefault();
+
+      resolve(true);
+    }
+
+    if (window.eventSender) {
+      mouseMoveToCenter(dragged);
+      eventSender.mouseDown();
+      setTimeout(() => {
+        mouseMoveToCenter(dropZone);
+        eventSender.mouseUp();
+      }, 100);
+    }
+  }).then(() => t.step(() => {
+    assert_equals(gotDragStart, true,
+        'dragstart event should fire for all drags');
+    if (gotDragStart) {
+      assert_true(dragStartTarget.classList.contains('dragged'),
+          'the dragged element should have the class "dragged"');
+      assert_equals(dragStartEffect, 'none',
+          'dataTransfer.dropEffect must always default to "none" in dragstart');
+      assert_equals(dragStartUriList, params.dragStartUriList,
+          'incorrect dataTransfer.getData("text/uri-list") in dragstart');
+      assert_array_equals(dragStartTypes, params.dragStartTypes,
+          'incorrect dataTransfer types in dragstart');
+    }
+
+    if (gotDrop) {
+      assert_equals(dropEffect, 'none',
+          'dataTransfer.dropEffect must always default to "none" in drop');
+    }
+  }));
+}
+
+if (window.testRunner)
+  testRunner.dumpDragImage();