Remove Document::frame_ and use dom_window_->GetFrame()

In cases where the LocalDOMWindow* is what we want, or where we just
need to null-check the frame, use dom_window_ instead of frame_. All
others now call GetFrame().

Bug: 1080735
Change-Id: Ib6b37e16f05d675e19212c38e474d5ad56e4c182
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2212782Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Nate Chapin <japhet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771862}

third_party/blink/renderer/core/dom/document.h

@@ -574,8 +574,8 @@ class CORE_EXPORT Document : public ContainerNode,
   DocumentState* GetDocumentState() const;
   void SetStateForNewControls(const Vector<String>&);
 
-  LocalFrameView* View() const;                    // can be null
-  LocalFrame* GetFrame() const { return frame_; }  // can be null
+  LocalFrameView* View() const;  // can be null
+  LocalFrame* GetFrame() const;  // can be null
   // Returns frame_ for current document, or if this is an HTML import, master
   // document's frame_, if any.  Can be null.
   // TODO(kochi): Audit usage of this interface (crbug.com/746150).
@@ -1856,7 +1856,6 @@ class CORE_EXPORT Document : public ContainerNode,
   PendingSheetLayout pending_sheet_layout_;
 
   Member<WindowAgentFactory> window_agent_factory_;
-  Member<LocalFrame> frame_;
   Member<LocalDOMWindow> dom_window_;
   Member<HTMLImportsController> imports_controller_;