Bug 1815913 - Init nsImageMap more eagerly r=emilio

Since we are initializing nsImageMap lazily, it's possible for area elements
stays non-focusable when autofocus code tries to focus it. So to fix
this, we need to ensure nsImageMap is initialized early enough.

Differential Revision: https://phabricator.services.mozilla.com/D168166

dom/base/nsIContentInlines.h

@@ -44,9 +44,10 @@ inline bool nsIContent::IsInChromeDocument() const {
 inline void nsIContent::SetPrimaryFrame(nsIFrame* aFrame) {
   MOZ_ASSERT(IsInUncomposedDoc() || IsInShadowTree(), "This will end badly!");
 
-  // FIXME bug 749326
-  NS_ASSERTION(!aFrame || !mPrimaryFrame || aFrame == mPrimaryFrame,
-               "Losing track of existing primary frame");
+  // <area> is known to trigger this, see bug 749326 and bug 135040.
+  MOZ_ASSERT(IsHTMLElement(nsGkAtoms::area) || !aFrame || !mPrimaryFrame ||
+                 aFrame == mPrimaryFrame,
+             "Losing track of existing primary frame");
 
   if (aFrame) {
     MOZ_ASSERT(!aFrame->IsPlaceholderFrame());

layout/generic/nsImageFrame.cpp

@@ -513,6 +513,9 @@ void nsImageFrame::Init(nsIContent* aContent, nsContainerFrame* aParent,
 
   mListener = new nsImageListener(this);
 
+  GetImageMap();  // Ensure to init the image map asap. This is important to
+                  // make <area> elements focusable.
+
   if (!gIconLoad) {
     LoadIcons(PresContext());
   }