Removing unused SetBrowserContext

This method is no longer used, and should be removed.

BUG=
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2046713002
Cr-Commit-Position: refs/heads/master@{#398216}

content/browser/frame_host/navigation_controller_impl.cc

@@ -256,11 +256,6 @@ BrowserContext* NavigationControllerImpl::GetBrowserContext() const {
   return browser_context_;
 }
 
-void NavigationControllerImpl::SetBrowserContext(
-    BrowserContext* browser_context) {
-  browser_context_ = browser_context;
-}
-
 void NavigationControllerImpl::Restore(
     int selected_navigation,
     RestoreType type,

content/browser/frame_host/navigation_controller_impl.h

@@ -42,7 +42,6 @@ class CONTENT_EXPORT NavigationControllerImpl
   // NavigationController implementation:
   WebContents* GetWebContents() const override;
   BrowserContext* GetBrowserContext() const override;
-  void SetBrowserContext(BrowserContext* browser_context) override;
   void Restore(int selected_navigation,
                RestoreType type,
                std::vector<std::unique_ptr<NavigationEntry>>* entries) override;

content/public/browser/navigation_controller.h

@@ -231,9 +231,8 @@ class NavigationController {
   // nullptr.
   virtual WebContents* GetWebContents() const = 0;
 
-  // Get/set the browser context for this controller. It can never be nullptr.
+  // Get the browser context for this controller. It can never be nullptr.
   virtual BrowserContext* GetBrowserContext() const = 0;
-  virtual void SetBrowserContext(BrowserContext* browser_context) = 0;
 
   // Initializes this NavigationController with the given saved navigations,
   // using |selected_navigation| as the currently loaded entry. Before this call