While screencasting a tab, do not disable rendering updates while hidden.

content/browser/web_contents/web_contents_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/web_contents/web_contents_impl.h"
 
 #include <utility>
 
 #include "base/command_line.h"
 #include "base/metrics/histogram.h"
@@ skipping 291 matching lines @@
       opener_(opener),
       ALLOW_THIS_IN_INITIALIZER_LIST(render_manager_(this, this, this)),
       is_loading_(false),
       crashed_status_(base::TERMINATION_STATUS_STILL_RUNNING),
       crashed_error_code_(0),
       waiting_for_response_(false),
       load_state_(net::LOAD_STATE_IDLE, string16()),
       upload_size_(0),
       upload_position_(0),
       displayed_insecure_content_(false),
-      capturing_contents_(false),
+      capturing_count_(0),
       is_being_destroyed_(false),
       notify_disconnection_(false),
       dialog_manager_(NULL),
       is_showing_before_unload_dialog_(false),
       opener_web_ui_type_(WebUI::kNoWebUI),
       closed_by_user_gesture_(false),
       minimum_zoom_percent_(static_cast<int>(kMinimumZoomFactor * 100)),
       maximum_zoom_percent_(static_cast<int>(kMaximumZoomFactor * 100)),
       temporary_zoom_settings_(false),
       content_restrictions_(0),
@@ skipping 678 matching lines @@
 }
 
 const std::string& WebContentsImpl::GetEncoding() const {
   return encoding_;
 }
 
 bool WebContentsImpl::DisplayedInsecureContent() const {
   return displayed_insecure_content_;
 }
 
 void WebContentsImpl::SetCapturingContents(bool cap) {

[ncarter (slow), 2013/02/04 22:13:43]

It seems a little risky to have a method named SetSomething(bool) that is not
idempotent. Would any of the following be an improvement:

AddCaptureSession() / RemoveCaptureSession()
IncrementCapturerCount() / DecrementCapturerCount()
RegisterCapturer() / UnregisterCapturer()

?

-  capturing_contents_ = cap;
+  capturing_count_ += cap ? +1 : -1;
+  DVLOG(1) << "There are now " << capturing_count_
+           << " capturing(s) of WebContentsImpl@" << this;
+  DCHECK_LE(0, capturing_count_);
 }
 
 bool WebContentsImpl::IsCrashed() const {
   return (crashed_status_ == base::TERMINATION_STATUS_PROCESS_CRASHED ||
           crashed_status_ == base::TERMINATION_STATUS_ABNORMAL_TERMINATION ||
           crashed_status_ == base::TERMINATION_STATUS_PROCESS_WAS_KILLED);
 }
 
 void WebContentsImpl::SetIsCrashed(base::TerminationStatus status,
                                    int error_code) {
@@ skipping 46 matching lines @@
   }
 
   bool is_visible = true;
   NotificationService::current()->Notify(
       NOTIFICATION_WEB_CONTENTS_VISIBILITY_CHANGED,
       Source<WebContents>(this),
       Details<bool>(&is_visible));
 }
 
 void WebContentsImpl::WasHidden() {
-  if (!capturing_contents_) {
+  // If there are entities capturing screenshots or video (e.g., mirroring),
+  // don't activate the "disable rendering" optimization.
+  if (capturing_count_ == 0) {
     // |GetRenderViewHost()| can be NULL if the user middle clicks a link to
-    // open a tab in then background, then closes the tab before selecting it.
+    // open a tab in the background, then closes the tab before selecting it.
     // This is because closing the tab calls WebContentsImpl::Destroy(), which
     // removes the |GetRenderViewHost()|; then when we actually destroy the
     // window, OnWindowPosChanged() notices and calls WasHidden() (which
     // calls us).
     RenderWidgetHostViewPort* rwhv =
         RenderWidgetHostViewPort::FromRWHV(GetRenderWidgetHostView());
     if (rwhv)
       rwhv->WasHidden();
   }
 
@@ skipping 2358 matching lines @@
 
 BrowserPluginGuest* WebContentsImpl::GetBrowserPluginGuest() {
   return browser_plugin_guest_.get();
 }
 
 BrowserPluginEmbedder* WebContentsImpl::GetBrowserPluginEmbedder() {
   return browser_plugin_embedder_.get();
 }
 
 }  // namespace content