Bug 1402845 - Fix panelview sizing when customRectGetter is used. r=mikedeboer,Paolo

* The extension content drives the sizing of the browser and popup that contains it via the Extension:BrowserResized message. The ignoreResizes property throttles/debounces this initially, stashing the dimensions received rather than triggering resize of the popup for every message. When the popup is a subview and fixedWidth, we ignore width but *do* want to use the stashed height value.

* Until the panel is given visibility, it has 0 height, so after setting visibility, wait until the next refresh-driver tick before measuring any header which should get added to the overall view height

MozReview-Commit-ID: AgcruVb9QPA

--HG--
extra : rebase_source : 429503a7d38559cc8670a3205b3290b8e0bbbfa2

browser/components/customizableui/PanelMultiView.jsm

@@ -875,11 +875,15 @@ var PanelMultiView = class extends AssociatedToNode {
       let width = prevPanelView.knownWidth;
       let height = prevPanelView.knownHeight;
       viewRect = Object.assign({height, width}, viewNode.customRectGetter());
+      nextPanelView.visible = true;
+      // Until the header is visible, it has 0 height.
+      // Wait for layout before measuring it
       let header = viewNode.firstChild;
       if (header && header.classList.contains("panel-header")) {
-        viewRect.height += this._dwu.getBoundsWithoutFlushing(header).height;
+        viewRect.height += await window.promiseDocumentFlushed(() => {
+          return this._dwu.getBoundsWithoutFlushing(header).height;
+        });
       }
-      nextPanelView.visible = true;
       await nextPanelView.descriptionHeightWorkaround();
     } else {
       this._offscreenViewStack.style.minHeight = olderView.knownHeight + "px";

browser/components/extensions/ExtensionPopups.jsm

@@ -512,7 +512,10 @@ class ViewPopup extends BasePopup {
     this.browser.swapDocShells(browser);
     this.destroyBrowser(browser);
 
-    if (this.dimensions && !this.fixedWidth) {
+    if (this.dimensions) {
+      if (this.fixedWidth) {
+        delete this.dimensions.width;
+      }
       this.resizeBrowser(this.dimensions);
     }