content: Add switch to disable new content rendering timeout.

In e.g. some headless environments, we care about deterministic
rendering results. As the new content rendering timeout can affect page
rendering, we'd like a way to disable it.

This patch adds a command line switch to that effect.

Change-Id: Ib0c09aa57df82665ffb4f1290c8ad5d2761aa7bf
Bug: 776292
Reviewed-on: https://chromium-review.googlesource.com/725324
Commit-Queue: Eric Seckler <eseckler@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510030}

content/browser/renderer_host/render_widget_host_impl.cc

@@ -390,9 +390,12 @@ RenderWidgetHostImpl::RenderWidgetHostImpl(RenderWidgetHostDelegate* delegate,
                    weak_factory_.GetWeakPtr())));
   }
 
-  new_content_rendering_timeout_.reset(new TimeoutMonitor(
-      base::Bind(&RenderWidgetHostImpl::ClearDisplayedGraphics,
-                 weak_factory_.GetWeakPtr())));
+  if (!base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kDisableNewContentRenderingTimeout)) {
+    new_content_rendering_timeout_.reset(new TimeoutMonitor(
+        base::Bind(&RenderWidgetHostImpl::ClearDisplayedGraphics,
+                   weak_factory_.GetWeakPtr())));
+  }
 
   const base::CommandLine& command_line =
       *base::CommandLine::ForCurrentProcess();
@@ -1080,6 +1083,10 @@ void RenderWidgetHostImpl::LogHangMonitorUnresponsive() {
 void RenderWidgetHostImpl::StartNewContentRenderingTimeout(
     uint32_t next_source_id) {
   current_content_source_id_ = next_source_id;
+
+  if (!new_content_rendering_timeout_)
+    return;
+
   // It is possible for a compositor frame to arrive before the browser is
   // notified about the page being committed, in which case no timer is
   // necessary.
@@ -2704,7 +2711,8 @@ void RenderWidgetHostImpl::SubmitCompositorFrame(
 
   // After navigation, if a frame belonging to the new page is received, stop
   // the timer that triggers clearing the graphics of the last page.
-  if (last_received_content_source_id_ >= current_content_source_id_ &&
+  if (new_content_rendering_timeout_ &&
+      last_received_content_source_id_ >= current_content_source_id_ &&
       new_content_rendering_timeout_->IsRunning()) {
     new_content_rendering_timeout_->Stop();
   }

content/public/common/content_switches.cc

@@ -208,6 +208,11 @@ const char kDisableMojoLocalStorage[] = "disable-mojo-local-storage";
 // Disables usage of the namespace sandbox.
 const char kDisableNamespaceSandbox[]       = "disable-namespace-sandbox";
 
+// Disables clearing the rendering output of a renderer when it didn't commit
+// new output for a while after a top-frame navigation.
+const char kDisableNewContentRenderingTimeout[] =
+    "disable-new-content-rendering-timeout";
+
 // Disables the Web Notification and the Push APIs.
 const char kDisableNotifications[]          = "disable-notifications";
 

content/public/common/content_switches.h

@@ -74,6 +74,7 @@ CONTENT_EXPORT extern const char kDisableLocalStorage[];
 CONTENT_EXPORT extern const char kDisableLogging[];
 CONTENT_EXPORT extern const char kDisableMojoLocalStorage[];
 CONTENT_EXPORT extern const char kDisableNamespaceSandbox[];
+CONTENT_EXPORT extern const char kDisableNewContentRenderingTimeout[];
 CONTENT_EXPORT extern const char kDisableNotifications[];
 CONTENT_EXPORT extern const char kDisableOriginTrialControlledBlinkFeatures[];
 CONTENT_EXPORT extern const char kDisablePartialRaster[];