Update HostZoomMap event subscription when RenderViewHost changes.

Each ZoomController is associated with a WebContents and a HostZoomMap.
However, it is possible that a WebContents can, as it navigates, change
its StoragePartition, and therefore its HostZoomMap. This CL monitors
WebContentsObserver for changes in RenderViewHost, and updates the
HostZoomMap subscription if the HostZoomMap changes.

BUG=438979

Review URL: https://codereview.chromium.org/767293006

Cr-Commit-Position: refs/heads/master@{#308585}

2 files changed, 21 insertions, 4 deletions

diff --git a/components/ui/zoom/zoom_controller.cc b/components/ui/zoom/zoom_controller.cc
index cc07e31..a2e49a8 100644
--- a/components/ui/zoom/zoom_controller.cc
+++ b/components/ui/zoom/zoom_controller.cc
@@ -26,11 +26,10 @@ ZoomController::ZoomController(content::WebContents* web_contents)
       zoom_mode_(ZOOM_MODE_DEFAULT),
       zoom_level_(1.0),
       browser_context_(web_contents->GetBrowserContext()) {
-  content::HostZoomMap* host_zoom_map =
-      content::HostZoomMap::GetForWebContents(web_contents);
-  zoom_level_ = host_zoom_map->GetDefaultZoomLevel();
+  host_zoom_map_ = content::HostZoomMap::GetForWebContents(web_contents);
+  zoom_level_ = host_zoom_map_->GetDefaultZoomLevel();
 
-  zoom_subscription_ = host_zoom_map->AddZoomLevelChangedCallback(
+  zoom_subscription_ = host_zoom_map_->AddZoomLevelChangedCallback(
       base::Bind(&ZoomController::OnZoomLevelChanged, base::Unretained(this)));
 
   UpdateState(std::string());
@@ -253,6 +252,20 @@ void ZoomController::WebContentsDestroyed() {
   observers_.Clear();
 }
 
+void ZoomController::RenderFrameHostChanged(
+    content::RenderFrameHost* old_host,
+    content::RenderFrameHost* new_host) {
+  // If our associated HostZoomMap changes, update our event subscription.
+  content::HostZoomMap* new_host_zoom_map =
+      content::HostZoomMap::GetForWebContents(web_contents());
+  if (new_host_zoom_map == host_zoom_map_)
+    return;
+
+  host_zoom_map_ = new_host_zoom_map;
+  zoom_subscription_ = host_zoom_map_->AddZoomLevelChangedCallback(
+      base::Bind(&ZoomController::OnZoomLevelChanged, base::Unretained(this)));
+}
+
 void ZoomController::OnZoomLevelChanged(
     const content::HostZoomMap::ZoomLevelChange& change) {
   UpdateState(change.host);
diff --git a/components/ui/zoom/zoom_controller.h b/components/ui/zoom/zoom_controller.h
index 5814345..f661ba4 100644
--- a/components/ui/zoom/zoom_controller.h
+++ b/components/ui/zoom/zoom_controller.h
@@ -140,6 +140,8 @@ class ZoomController : public content::WebContentsObserver,
       const content::LoadCommittedDetails& details,
       const content::FrameNavigateParams& params) override;
   void WebContentsDestroyed() override;
+  void RenderFrameHostChanged(content::RenderFrameHost* old_host,
+                              content::RenderFrameHost* new_host) override;
 
  protected:
   // Protected for testing.
@@ -176,6 +178,8 @@ class ZoomController : public content::WebContentsObserver,
   ObserverList<ZoomObserver> observers_;
 
   content::BrowserContext* browser_context_;
+  // Keep track of the HostZoomMap we're currently subscribed to.
+  content::HostZoomMap* host_zoom_map_;
 
   scoped_ptr<content::HostZoomMap::Subscription> zoom_subscription_;