Bug 1709614. Allow the double tap heuristic to look at grand parent for table cells. r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D114361

gfx/layers/apz/test/mochitest/helper_doubletap_zoom_tablecell.html

@@ -12,23 +12,30 @@
 async function test() {
   let useTouchpad = (location.search == "?touchpad");
 
-  var resolution = getResolution();
+  let resolution = getResolution();
   ok(resolution > 0,
      "The initial_resolution is " + resolution + ", which is some sane value");
 
   // Check that double-tapping does not zoom in
   info("sending first double tap");
   await doubleTapOn(document.getElementById("target1"), 10, 10, useTouchpad);
-  var prev_resolution = resolution;
+  let prev_resolution = resolution;
   resolution = getResolution();
   ok(resolution == prev_resolution, "The first double-tap did not change the resolution: " + resolution);
 
-  // Check that double-tapping does zoom in
+  // Check that double-tapping does not zoom in
   info("sending second double tap");
   await doubleTapOn(document.getElementById("target2"), 10, 10, useTouchpad);
   prev_resolution = resolution;
   resolution = getResolution();
-  ok(resolution > prev_resolution, "The second double-tap has increased the resolution to " + resolution);
+  ok(resolution == prev_resolution, "The second double-tap did not change the resolution: " + resolution);
+
+  // Check that double-tapping does zoom in
+  info("sending third double tap");
+  await doubleTapOn(document.getElementById("target3"), 10, 10, useTouchpad);
+  prev_resolution = resolution;
+  resolution = getResolution();
+  ok(resolution > prev_resolution, "The third double-tap has increased the resolution to " + resolution);
 }
 
 waitUntilApzStable()
@@ -78,7 +85,21 @@ waitUntilApzStable()
     </thead>
     <tbody>
         <tr>
-            <td id="target2" class="big">The table body</td>
+            <td class="small"><div class="small"><div id="target2" class="small">The table body</div></div></td>
+            <td>with two columns</td>
+        </tr>
+    </tbody>
+</table>
+
+<table>
+    <thead>
+        <tr>
+            <th colspan="2">The table header</th>
+        </tr>
+    </thead>
+    <tbody>
+        <tr>
+            <td id="target3" class="big">The table body</td>
             <td>with two columns</td>
         </tr>
     </tbody>

gfx/layers/apz/util/DoubleTapToZoom.cpp

@@ -72,7 +72,7 @@ static already_AddRefed<dom::Element> ElementFromPoint(
   return nullptr;
 }
 
-// Get table cell from element or parent.
+// Get table cell from element, parent or grand parent.
 static dom::Element* GetNearbyTableCell(
     const nsCOMPtr<dom::Element>& aElement) {
   nsTableCellFrame* tableCell = do_QueryFrame(aElement->GetPrimaryFrame());
@@ -84,6 +84,12 @@ static dom::Element* GetNearbyTableCell(
     if (tableCell) {
       return parent;
     }
+    if (dom::Element* grandParent = parent->GetFlattenedTreeParentElement()) {
+      tableCell = do_QueryFrame(grandParent->GetPrimaryFrame());
+      if (tableCell) {
+        return grandParent;
+      }
+    }
   }
   return nullptr;
 }