Bug 1645520 - Ensure an MVM operating in VisualViewportOnly mode knows about display resizes. r=tnikkel

This is important because if the apz.allow_zooming pref is enabled (and
eventually even without that pref), VisualViewportOnly-type MVMs do set
the visual viewport size based on the display size and zoom, and so need
to be updated when those change.

Differential Revision: https://phabricator.services.mozilla.com/D79594

layout/base/MobileViewportManager.cpp

@@ -540,9 +540,29 @@ void MobileViewportManager::RefreshVisualViewportSize() {
   ScreenIntSize displaySize = ViewAs<ScreenPixel>(
       mDisplaySize, PixelCastJustification::LayoutDeviceIsScreenForBounds);
 
+  if (displaySize.width == 0 || displaySize.height == 0) {
+    return;
+  }
+
   UpdateVisualViewportSize(displaySize, GetZoom());
 }
 
+void MobileViewportManager::NotifyResizeReflow() {
+  // If there's a resize-reflow, the visual viewport may need to be recomputed
+  // for a new display size, so let's do that.
+  if (Maybe<LayoutDeviceIntSize> newDisplaySize =
+          mContext->GetContentViewerSize()) {
+    // Note that we intentionally don't short-circuit here if the display size
+    // (in LD units) is unchanged, because a resize-reflow may also be triggered
+    // by a change in the CSS/LD pixel ratio which would affect GetZoom() and
+    // therefore the computed visual viewport.
+    mDisplaySize = *newDisplaySize;
+    MVM_LOG("%p: Display size updated to %s\n", this,
+            Stringify(mDisplaySize).c_str());
+    RefreshVisualViewportSize();
+  }
+}
+
 void MobileViewportManager::RefreshViewportSize(bool aForceAdjustResolution) {
   // This function gets called by the various triggers that may result in a
   // change of the CSS viewport. In some of these cases (e.g. the meta-viewport

layout/base/MobileViewportManager.h

@@ -74,6 +74,12 @@ class MobileViewportManager final : public nsIDOMEventListener,
   void SetRestoreResolution(float aResolution);
 
  public:
+  /* Notify the MobileViewportManager that a resize-reflow is about to happen,
+   * possibly indicating a change in the display size or some other quantity
+   * that the visual viewport depends on.
+   */
+  void NotifyResizeReflow();
+
   /* Notify the MobileViewportManager that a reflow was requested in the
    * presShell.*/
   void RequestReflow(bool aForceAdjustResolution);

layout/base/PresShell.cpp

@@ -1955,6 +1955,9 @@ nsresult PresShell::ResizeReflow(nscoord aWidth, nscoord aHeight,
     mMobileViewportManager->RequestReflow(false);
     return NS_OK;
   }
+  if (mMobileViewportManager) {
+    mMobileViewportManager->NotifyResizeReflow();
+  }
 
   return ResizeReflowIgnoreOverride(aWidth, aHeight, aOptions);
 }

testing/web-platform/meta/css/css-scroll-anchoring/start-edge-in-block-layout-direction.html.ini

@@ -1,26 +0,0 @@
-[start-edge-in-block-layout-direction.html]
-  [Vertical-RL LTR.]
-    expected:
-      if (os == "android") and not e10s: FAIL
-      if (os == "android") and e10s: FAIL
-
-  [Horizontal RTL.]
-    expected:
-      if (os == "android") and not e10s: FAIL
-      if (os == "android") and e10s: FAIL
-
-  [Vertical-LR LTR.]
-    expected:
-      if (os == "android") and not e10s: FAIL
-      if (os == "android") and e10s: FAIL
-
-  [Vertical-RL RTL.]
-    expected:
-      if (os == "android") and not e10s: FAIL
-      if (os == "android") and e10s: FAIL
-
-  [Vertical-LR RTL.]
-    expected:
-      if (os == "android") and not e10s: FAIL
-      if (os == "android") and e10s: FAIL
-