Bug 1594529: Infer nsDocShell::IsFrame from BrowsingContext. r=nika

This fixes the content policy type for document loads in these frames, where
the explicit mIsFrame flag was not set, due to DocShell creation taking a
different code path in remote frames than in in-process frames.

Differential Revision: https://phabricator.services.mozilla.com/D52093

--HG--
extra : moz-landing-system : lando

docshell/base/nsDocShell.cpp

@@ -388,7 +388,6 @@ nsDocShell::nsDocShell(BrowsingContext* aBrowsingContext,
       mHasLoadedNonBlankURI(false),
       mBlankTiming(false),
       mTitleValidForCurrentURI(false),
-      mIsFrame(false),
       mSkipBrowsingContextDetachOnDestroy(false),
       mWatchedByDevtools(false),
       mIsNavigating(false) {
@@ -12088,8 +12087,6 @@ nsresult nsDocShell::EnsureFind() {
   return NS_OK;
 }
 
-bool nsDocShell::IsFrame() { return mIsFrame; }
-
 NS_IMETHODIMP
 nsDocShell::IsBeingDestroyed(bool* aDoomed) {
   NS_ENSURE_ARG(aDoomed);

docshell/base/nsDocShell.h

@@ -348,8 +348,6 @@ class nsDocShell final : public nsDocLoader,
   void SetInFrameSwap(bool aInSwap) { mInFrameSwap = aInSwap; }
   bool InFrameSwap();
 
-  void SetIsFrame() { mIsFrame = true; };
-
   const mozilla::Encoding* GetForcedCharset() { return mForcedCharset; }
 
   mozilla::HTMLEditor* GetHTMLEditorInternal();
@@ -971,7 +969,7 @@ class nsDocShell final : public nsDocLoader,
   void RecomputeCanExecuteScripts();
   void ClearFrameHistory(nsISHEntry* aEntry);
   void UpdateGlobalHistoryTitle(nsIURI* aURI);
-  bool IsFrame();
+  bool IsFrame() { return mBrowsingContext->GetParent(); }
   bool CanSetOriginAttributes();
   bool ShouldBlockLoadingForBackButton();
   bool ShouldDiscardLayoutState(nsIHttpChannel* aChannel);
@@ -1330,8 +1328,6 @@ class nsDocShell final : public nsDocLoader,
   // This flag indicates when the title is valid for the current URI.
   bool mTitleValidForCurrentURI : 1;
 
-  bool mIsFrame : 1;
-
   // If mSkipBrowsingContextDetachOnDestroy is set to true, then when the
   // docshell is destroyed, the browsing context will not be detached. This is
   // for cases where we want to preserve the BC for future use.

dom/base/nsFrameLoader.cpp

@@ -2133,8 +2133,6 @@ nsresult nsFrameLoader::MaybeCreateDocShell() {
 
   if (OwnerIsMozBrowserFrame()) {
     docShell->SetFrameType(nsIDocShell::FRAME_TYPE_BROWSER);
-  } else if (mBrowsingContext->GetParent()) {
-    docShell->SetIsFrame();
   }
 
   // Apply sandbox flags even if our owner is not an iframe, as this copies