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

docshell/base/nsDocShell.h

@@ -360,8 +360,6 @@ 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();
@@ -1002,7 +1000,7 @@ 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);
@@ -1333,8 +1331,6 @@ class nsDocShell final : public nsDocLoader,
   // This flag indicates when the title is valid for the current URI.
   bool mTitleValidForCurrentURI : 1;
 
-  bool mIsFrame : 1;
-
   // If mWillChangeProcess is set to true, then when the docshell is destroyed,
   // we prepare the browsing context to change process.
   bool mWillChangeProcess : 1;