Expose Resume() in RenderProcessHost.

content/renderer/render_thread_impl.cc

Index: content/renderer/render_thread_impl.cc
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index 6ca91bed3a272b90adb6bde4aa7d0e2ec2715f07..a041d68de37935a326687db6c18c31df3c53bc9d 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -1766,7 +1766,7 @@ void RenderThreadImpl::OnProcessBackgrounded(bool backgrounded) {
 
 void RenderThreadImpl::OnProcessPurgeAndSuspend() {
   ChildThreadImpl::OnProcessPurgeAndSuspend();
-  if (is_renderer_suspended_)
+  if (is_renderer_suspended_ || !RendererIsHidden())
     return;
   // TODO(hajimehoshi): Implement purging e.g. cache (crbug/607077)
   is_renderer_suspended_ = true;
@@ -1877,6 +1877,15 @@ void RenderThreadImpl::RecordPurgeAndSuspendMetrics() const {
                               1024 / 1024);
 }
 
+void RenderThreadImpl::OnProcessResume() {
+  ChildThreadImpl::OnProcessResume();
+  if (!is_renderer_suspended_)

[dcheng, 2016/10/27 03:41:58]

Do we expect this conditional to be hit in practice? I would expect the browser
to have perfect knowledge of the state, or can it get out of sync?

[tasak, 2016/10/27 04:49:40]

Replaced the "if" with DCHECK.

TabManager will have the state, i.e. RUNNING, SUSPENDED, and RESUMED, and change
RenderThreadImpl's state by using IPC messages.

+    return;
+
+  is_renderer_suspended_ = false;
+  renderer_scheduler_->ResumeRenderer();
+}
+
 scoped_refptr<gpu::GpuChannelHost> RenderThreadImpl::EstablishGpuChannelSync() {
   TRACE_EVENT0("gpu", "RenderThreadImpl::EstablishGpuChannelSync");