[DevTools] Throttle device emulation with respect to produced frames.

We do not issue new device emulation command until the frame arrives (guarded by timeout).

BUG=none

Review URL: https://codereview.chromium.org/1436983003

Cr-Commit-Position: refs/heads/master@{#359254}

3 files changed, 45 insertions, 6 deletions

diff --git a/content/browser/devtools/protocol/emulation_handler.cc b/content/browser/devtools/protocol/emulation_handler.cc
index cae9f00..9659991 100644
--- a/content/browser/devtools/protocol/emulation_handler.cc
+++ b/content/browser/devtools/protocol/emulation_handler.cc
@@ -35,11 +35,19 @@ ui::GestureProviderConfigType TouchEmulationConfigurationToType(
   return result;
 }
 
+// When continuously applying device emulation, we wait for compositor frame
+// before applying new values. If the frame does not arrive during this
+// timeout, we proceed anyway.
+const int kFrameTimeoutMs = 67;
+
 }  // namespace
 
 EmulationHandler::EmulationHandler(page::PageHandler* page_handler)
     : touch_emulation_enabled_(false),
       device_emulation_enabled_(false),
+      device_emulation_needs_update_(false),
+      device_emulation_waiting_for_frame_(false),
+      frame_timer_(new base::Timer(false, false)),
       page_handler_(page_handler),
       host_(nullptr)
 {
@@ -59,14 +67,14 @@ void EmulationHandler::SetRenderFrameHost(RenderFrameHostImpl* host) {
 
   host_ = host;
   UpdateTouchEventEmulationState();
-  UpdateDeviceEmulationState();
+  ApplyDeviceEmulationState();
 }
 
 void EmulationHandler::Detached() {
   touch_emulation_enabled_ = false;
   device_emulation_enabled_ = false;
   UpdateTouchEventEmulationState();
-  UpdateDeviceEmulationState();
+  ApplyDeviceEmulationState();
 }
 
 Response EmulationHandler::SetGeolocationOverride(
@@ -192,7 +200,7 @@ Response EmulationHandler::SetDeviceMetricsOverride(
 
   device_emulation_enabled_ = true;
   device_emulation_params_ = params;
-  UpdateDeviceEmulationState();
+  DeviceEmulationNeedsUpdate();
   return Response::OK();
 }
 
@@ -201,7 +209,7 @@ Response EmulationHandler::ClearDeviceMetricsOverride() {
     return Response::OK();
 
   device_emulation_enabled_ = false;
-  UpdateDeviceEmulationState();
+  DeviceEmulationNeedsUpdate();
   return Response::OK();
 }
 
@@ -225,11 +233,31 @@ void EmulationHandler::UpdateTouchEventEmulationState() {
     GetWebContents()->SetForceDisableOverscrollContent(enabled);
 }
 
-void EmulationHandler::UpdateDeviceEmulationState() {
+void EmulationHandler::DeviceEmulationNeedsUpdate() {
+  device_emulation_needs_update_ = true;
+  if (!device_emulation_waiting_for_frame_)
+    ApplyDeviceEmulationState();
+}
+
+void EmulationHandler::OnSwapCompositorFrame() {
+  frame_timer_->Stop();
+  device_emulation_waiting_for_frame_ = false;
+  if (device_emulation_needs_update_)
+    ApplyDeviceEmulationState();
+}
+
+void EmulationHandler::ApplyDeviceEmulationState() {
+  device_emulation_needs_update_ = false;
   RenderWidgetHostImpl* widget_host =
       host_ ? host_->GetRenderWidgetHost() : nullptr;
   if (!widget_host)
     return;
+  device_emulation_waiting_for_frame_ = true;
+  frame_timer_->Start(
+      FROM_HERE,
+      base::TimeDelta::FromMilliseconds(kFrameTimeoutMs),
+      base::Bind(&EmulationHandler::OnSwapCompositorFrame,
+                 base::Unretained(this)));
   if (device_emulation_enabled_) {
     widget_host->Send(new ViewMsg_EnableDeviceEmulation(
         widget_host->GetRoutingID(), device_emulation_params_));
diff --git a/content/browser/devtools/protocol/emulation_handler.h b/content/browser/devtools/protocol/emulation_handler.h
index c2a4bd3..4f1e26f 100644
--- a/content/browser/devtools/protocol/emulation_handler.h
+++ b/content/browser/devtools/protocol/emulation_handler.h
@@ -5,6 +5,7 @@
 #ifndef CONTENT_BROWSER_DEVTOOLS_PROTOCOL_EMULATION_HANDLER_H_
 #define CONTENT_BROWSER_DEVTOOLS_PROTOCOL_EMULATION_HANDLER_H_
 
+#include "base/timer/timer.h"
 #include "content/browser/devtools/protocol/devtools_protocol_dispatcher.h"
 #include "content/browser/devtools/protocol/page_handler.h"
 #include "third_party/WebKit/public/web/WebDeviceEmulationParams.h"
@@ -32,6 +33,7 @@ class EmulationHandler : public page::PageHandler::ScreencastListener {
 
   void SetRenderFrameHost(RenderFrameHostImpl* host);
   void Detached();
+  void OnSwapCompositorFrame();
 
   Response SetGeolocationOverride(double* latitude,
                                   double* longitude,
@@ -59,13 +61,18 @@ class EmulationHandler : public page::PageHandler::ScreencastListener {
  private:
   WebContentsImpl* GetWebContents();
   void UpdateTouchEventEmulationState();
-  void UpdateDeviceEmulationState();
+
+  void DeviceEmulationNeedsUpdate();
+  void ApplyDeviceEmulationState();
 
   bool touch_emulation_enabled_;
   std::string touch_emulation_configuration_;
 
   bool device_emulation_enabled_;
   blink::WebDeviceEmulationParams device_emulation_params_;
+  bool device_emulation_needs_update_;
+  bool device_emulation_waiting_for_frame_;
+  scoped_ptr<base::Timer> frame_timer_;
 
   page::PageHandler* page_handler_;
   RenderFrameHostImpl* host_;
diff --git a/content/browser/devtools/render_frame_devtools_agent_host.cc b/content/browser/devtools/render_frame_devtools_agent_host.cc
index 71ab308..a9e7e7a 100644
--- a/content/browser/devtools/render_frame_devtools_agent_host.cc
+++ b/content/browser/devtools/render_frame_devtools_agent_host.cc
@@ -723,6 +723,8 @@ void RenderFrameDevToolsAgentHost::OnSwapCompositorFrame(
     page_handler_->OnSwapCompositorFrame(base::get<1>(param).metadata);
   if (input_handler_)
     input_handler_->OnSwapCompositorFrame(base::get<1>(param).metadata);
+  if (emulation_handler_)
+    emulation_handler_->OnSwapCompositorFrame();
   if (frame_trace_recorder_ && tracing_handler_->did_initiate_recording()) {
     frame_trace_recorder_->OnSwapCompositorFrame(
         current_ ? current_->host() : nullptr,
@@ -736,6 +738,8 @@ void RenderFrameDevToolsAgentHost::SynchronousSwapCompositorFrame(
     page_handler_->OnSynchronousSwapCompositorFrame(frame_metadata);
   if (input_handler_)
     input_handler_->OnSwapCompositorFrame(frame_metadata);
+  if (emulation_handler_)
+    emulation_handler_->OnSwapCompositorFrame();
   if (frame_trace_recorder_ && tracing_handler_->did_initiate_recording()) {
     frame_trace_recorder_->OnSynchronousSwapCompositorFrame(
         current_ ? current_->host() : nullptr,