Hide a TabContents's RenderViewHost while prerendering.

Should prevent offscreen drawing before display, except
in cases of WebGL, Canvas2D, and the like.

BUG=none
Test=PrerenderBrowserTest.*

Review URL: http://codereview.chromium.org/6975004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@85021 0039d316-1c4b-4281-b951-d872f2087c98

4 files changed, 80 insertions, 8 deletions

diff --git a/chrome/browser/prerender/prerender_browsertest.cc b/chrome/browser/prerender/prerender_browsertest.cc
index a8b274f..2a11291 100644
--- a/chrome/browser/prerender/prerender_browsertest.cc
+++ b/chrome/browser/prerender/prerender_browsertest.cc
@@ -20,6 +20,7 @@
 #include "chrome/test/ui_test_utils.h"
 #include "content/browser/renderer_host/render_view_host.h"
 #include "content/browser/tab_contents/tab_contents.h"
+#include "content/common/notification_service.h"
 #include "grit/generated_resources.h"
 #include "net/url_request/url_request_context.h"
 #include "net/url_request/url_request_context_getter.h"
@@ -62,17 +63,28 @@ class TestPrerenderContents : public PrerenderContents {
       : PrerenderContents(prerender_manager, profile, url, referrer),
         number_of_loads_(0),
         expected_number_of_loads_(number_of_loads),
-        expected_final_status_(expected_final_status) {
+        expected_final_status_(expected_final_status),
+        was_hidden_(false),
+        was_shown_(false) {
   }
 
   virtual ~TestPrerenderContents() {
     EXPECT_EQ(expected_final_status_, final_status()) <<
         " when testing URL " << prerender_url().path();
+    // Prerendering RenderViewHosts should be hidden before the first
+    // navigation, so this should be happen for every PrerenderContents that's
+    // created, regardless of whether or not it's used.
+    EXPECT_TRUE(was_hidden_);
+
     // A used PrerenderContents will only be destroyed when we swap out
     // TabContents, at the end of a navigation caused by a call to
     // NavigateToURLImpl().
-    if (final_status() == FINAL_STATUS_USED)
+    if (final_status() == FINAL_STATUS_USED) {
+      EXPECT_TRUE(was_shown_);
       MessageLoopForUI::current()->Quit();
+    } else {
+      EXPECT_FALSE(was_shown_);
+    }
   }
 
   virtual void OnRenderViewGone(int status, int exit_code) OVERRIDE {
@@ -108,9 +120,44 @@ class TestPrerenderContents : public PrerenderContents {
   }
 
  private:
+  virtual void OnRenderViewHostCreated(
+      RenderViewHost* new_render_view_host) OVERRIDE {
+    // Used to make sure the RenderViewHost is hidden and, if used,
+    // subsequently shown.
+    notification_registrar().Add(
+        this,
+        NotificationType::RENDER_WIDGET_VISIBILITY_CHANGED,
+        Source<RenderWidgetHost>(new_render_view_host));
+    PrerenderContents::OnRenderViewHostCreated(new_render_view_host);
+  }
+
+  virtual void Observe(NotificationType type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details) OVERRIDE {
+    if (type.value ==
+        NotificationType::RENDER_WIDGET_VISIBILITY_CHANGED) {
+      bool is_visible = *Details<bool>(details).ptr();
+      if (!is_visible) {
+        was_hidden_ = true;
+      } else if (is_visible && was_hidden_) {
+        // Once hidden, a prerendered RenderViewHost should only be shown after
+        // being removed from the PrerenderContents for display.
+        EXPECT_FALSE(render_view_host());
+        was_shown_ = true;
+      }
+      return;
+    }
+    PrerenderContents::Observe(type, source, details);
+  }
+
   int number_of_loads_;
   int expected_number_of_loads_;
   FinalStatus expected_final_status_;
+  // Set to true when the prerendering RenderWidget is hidden.
+  bool was_hidden_;
+  // Set to true when the prerendering RenderWidget is shown, after having been
+  // hidden.
+  bool was_shown_;
 };
 
 // PrerenderManager that uses TestPrerenderContents.
diff --git a/chrome/browser/prerender/prerender_contents.cc b/chrome/browser/prerender/prerender_contents.cc
index 4a989bc..2f2ebd0 100644
--- a/chrome/browser/prerender/prerender_contents.cc
+++ b/chrome/browser/prerender/prerender_contents.cc
@@ -129,6 +129,8 @@ void PrerenderContents::StartPrerenderingOld(
   // Create the RenderView, so it can receive messages.
   render_view_host_->CreateRenderView(string16());
 
+  OnRenderViewHostCreated(render_view_host_);
+
   // Give the RVH a PrerenderRenderWidgetHostView, both so its size can be set
   // and so that the prerender can be cancelled under certain circumstances.
   PrerenderRenderWidgetHostView* view =
@@ -473,19 +475,29 @@ void PrerenderContents::Observe(NotificationType type,
     }
 
     case NotificationType::RENDER_VIEW_HOST_CREATED_FOR_TAB: {
-      // When a new RenderView is created for a prerendering TabContents,
-      // tell the new RenderView it's being used for prerendering before any
-      // navigations occur.  Note that this is always triggered before the
-      // first navigation, so there's no need to send the message just after the
-      // TabContents is created.
       if (prerender_contents_.get()) {
         DCHECK_EQ(Source<TabContents>(source).ptr(),
                   prerender_contents_->tab_contents());
 
         Details<RenderViewHost> new_render_view_host(details);
+        OnRenderViewHostCreated(new_render_view_host.ptr());
+
+        // When a new RenderView is created for a prerendering TabContents,
+        // tell the new RenderView it's being used for prerendering before any
+        // navigations occur.  Note that this is always triggered before the
+        // first navigation, so there's no need to send the message just after
+        // the TabContents is created.
         new_render_view_host->Send(
             new ViewMsg_SetIsPrerendering(new_render_view_host->routing_id(),
                                           true));
+
+        // Set the new TabContents and its RenderViewHost as hidden, to reduce
+        // resource usage.  This can only be done after the first call to
+        // LoadURL, so there's an actual RenderViewHost with a
+        // RenderWidgetHostView to hide.
+        //
+        // Done here to prevent a race with loading the page.
+        prerender_contents_->tab_contents()->HideContents();
       }
       break;
     }
@@ -586,6 +598,10 @@ void PrerenderContents::ShowCreatedFullscreenWidget(int route_id) {
   NOTIMPLEMENTED();
 }
 
+void PrerenderContents::OnRenderViewHostCreated(
+    RenderViewHost* new_render_view_host) {
+}
+
 void PrerenderContents::OnDidStartProvisionalLoadForFrame(int64 frame_id,
                                                           bool is_main_frame,
                                                           const GURL& url) {
diff --git a/chrome/browser/prerender/prerender_contents.h b/chrome/browser/prerender/prerender_contents.h
index a525756..2be7286 100644
--- a/chrome/browser/prerender/prerender_contents.h
+++ b/chrome/browser/prerender/prerender_contents.h
@@ -252,6 +252,14 @@ class PrerenderContents : public RenderViewHostDelegate,
 
   const GURL& prerender_url() const { return prerender_url_; }
 
+  NotificationRegistrar& notification_registrar() {
+    return notification_registrar_;
+  }
+
+  // Called whenever a RenderViewHost is created for prerendering.  Only called
+  // once the RenderViewHost has a RenderView and RenderWidgetHostView.
+  virtual void OnRenderViewHostCreated(RenderViewHost* new_render_view_host);
+
  private:
   // Needs to be able to call the constructor.
   friend class PrerenderContentsFactoryImpl;
diff --git a/chrome/browser/prerender/prerender_manager.cc b/chrome/browser/prerender/prerender_manager.cc
index 9aa02fd..c249477 100644
--- a/chrome/browser/prerender/prerender_manager.cc
+++ b/chrome/browser/prerender/prerender_manager.cc
@@ -445,10 +445,11 @@ bool PrerenderManager::MaybeUsePreloadedPageOld(TabContents* tab_contents,
 
   RenderViewHost* render_view_host =
       prerender_contents->render_view_host_mutable();
+  prerender_contents->set_render_view_host(NULL);
+
   // RenderViewHosts in PrerenderContents start out hidden.
   // Since we are actually using it now, restore it.
   render_view_host->WasRestored();
-  prerender_contents->set_render_view_host(NULL);
   render_view_host->Send(
       new ViewMsg_SetIsPrerendering(render_view_host->routing_id(), false));
   tab_contents->SwapInRenderViewHost(render_view_host);