Create Browser::FromWebContents.

This allows code to get the Browser from a WebContents
safely. Existing code doing blind casting from a
WebContentsDelegate is updated, and there are two
tab helpers on the way that will be using it.

BUG=none

Change-Id: Idea2fa9bd98d9a607bfc0a1ff9d2e88a0812a509
Reviewed-on: https://chromium-review.googlesource.com/612044Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#494092}

chrome/browser/prerender/prerender_browsertest.cc

@@ -472,7 +472,7 @@ class NewTabNavigationOrSwapObserver {
     WebContents* new_tab = content::Details<WebContents>(details).ptr();
     // Get the TabStripModel. Assume this is attached to a Browser.
     TabStripModel* tab_strip_model =
-        static_cast<Browser*>(new_tab->GetDelegate())->tab_strip_model();
+        Browser::FromWebContents(new_tab)->tab_strip_model();
     swap_observer_.reset(new NavigationOrSwapObserver(tab_strip_model,
                                                       new_tab));
     swap_observer_->set_did_start_loading();

chrome/browser/ui/browser.cc

@@ -278,6 +278,19 @@ const extensions::Extension* GetExtensionForOrigin(
 #endif
 }
 
+// Stores a pointer to the Browser in the WebContents.
+struct BrowserLink : public base::SupportsUserData::Data {
+  static const char kKey[];
+
+  explicit BrowserLink(Browser* browser) : browser(browser) {}
+  ~BrowserLink() override = default;
+
+  Browser* browser;
+};
+
+// static
+const char BrowserLink::kKey[] = "BrowserLink";
+
 }  // namespace
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -566,6 +579,13 @@ Browser::~Browser() {
     select_file_dialog_->ListenerDestroyed();
 }
 
+// static
+Browser* Browser::FromWebContents(content::WebContents* web_contents) {
+  const BrowserLink* link =
+      static_cast<BrowserLink*>(web_contents->GetUserData(&BrowserLink::kKey));
+  return link ? link->browser : nullptr;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 // Getters & Setters
 
@@ -2357,7 +2377,8 @@ bool Browser::CanCloseWithInProgressDownloads() {
 // Browser, Assorted utility functions (private):
 
 void Browser::SetAsDelegate(WebContents* web_contents, bool set_delegate) {
-  Browser* delegate = set_delegate ? this : NULL;
+  Browser* delegate = set_delegate ? this : nullptr;
+
   // WebContents...
   web_contents->SetDelegate(delegate);
 
@@ -2375,6 +2396,14 @@ void Browser::SetAsDelegate(WebContents* web_contents, bool set_delegate) {
     zoom::ZoomController::FromWebContents(web_contents)->RemoveObserver(this);
     content_translate_driver.RemoveObserver(this);
   }
+
+  // Update the back-link from the WebContents to Browser.
+  if (set_delegate) {
+    web_contents->SetUserData(BrowserLink::kKey,
+                              base::MakeUnique<BrowserLink>(this));
+  } else {
+    web_contents->RemoveUserData(BrowserLink::kKey);
+  }
 }
 
 void Browser::CloseFrame() {

chrome/browser/ui/browser.h

@@ -220,6 +220,10 @@ class Browser : public TabStripModelObserver,
   explicit Browser(const CreateParams& params);
   ~Browser() override;
 
+  // Returns the Browser that contains the specified WebContents. May return
+  // null if no Browser has that WebContents as a tab.
+  static Browser* FromWebContents(content::WebContents* web_contents);
+
   // Set overrides for the initial window bounds and maximized state.
   void set_override_bounds(const gfx::Rect& bounds) {
     override_bounds_ = bounds;