Revert "Remove kEnableSurfaceSynchronization switch."

This reverts commit 6d87f94.

Reason for revert: broke external frame control for headless.

Original change's description:
> Remove kEnableSurfaceSynchronization switch.
> 
> The switch is left over from before there was a base::Feature. All
> platforms except Android WebView have it enabled by default already so
> the remaining places the switch gets added aren't necessary.
> 
> Bug: 938947
> Change-Id: I9b375453fb6dc71f204d848d93fedb9da976103e
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1585478
> Commit-Queue: kylechar <kylechar@chromium.org>
> Reviewed-by: Antoine Labour <piman@chromium.org>
> Reviewed-by: Eric Seckler <eseckler@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#655235}

TBR=kylechar@chromium.org,piman@chromium.org,eseckler@chromium.org

Change-Id: I7664a077239641bbad2a555c0ad88d72cb77974b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 938947
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1590999
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#655511}

components/viz/common/features.cc

@@ -59,8 +59,10 @@ const base::Feature kRecordSkPicture{"RecordSkPicture",
                                      base::FEATURE_DISABLED_BY_DEFAULT};
 
 bool IsSurfaceSynchronizationEnabled() {
+  auto* command_line = base::CommandLine::ForCurrentProcess();
   return IsVizDisplayCompositorEnabled() ||
-         base::FeatureList::IsEnabled(kEnableSurfaceSynchronization);
+         base::FeatureList::IsEnabled(kEnableSurfaceSynchronization) ||
+         command_line->HasSwitch(switches::kEnableSurfaceSynchronization);
 }
 
 bool IsVizDisplayCompositorEnabled() {

components/viz/common/switches.cc

@@ -15,16 +15,17 @@ namespace switches {
 const char kDeadlineToSynchronizeSurfaces[] =
     "deadline-to-synchronize-surfaces";
 
-// Disables begin frame limiting in both cc scheduler and display scheduler.
-// Also implies --disable-gpu-vsync (see //ui/gl/gl_switches.h).
-const char kDisableFrameRateLimit[] = "disable-frame-rate-limit";
-
 // Enable compositing individual elements via hardware overlays when
 // permitted by device.
 // Setting the flag to "single-fullscreen" will try to promote a single
 // fullscreen overlay and use it as main framebuffer where possible.
 const char kEnableHardwareOverlays[] = "enable-hardware-overlays";
 
+// Enables multi-client Surface synchronization. In practice, this indicates
+// that LayerTreeHost expects to be given a valid viz::LocalSurfaceId provided
+// by the parent compositor.
+const char kEnableSurfaceSynchronization[] = "enable-surface-synchronization";
+
 // Enables inspecting Viz Display Compositor objects. Default port is 9229.
 // For local inspection use chrome://inspect#other
 const char kEnableVizDevTools[] = "enable-viz-devtools";
@@ -41,6 +42,10 @@ const char kRunAllCompositorStagesBeforeDraw[] =
 // hit-test data coming from surface layer.
 const char kUseVizHitTestSurfaceLayer[] = "use-viz-hit-test-surface-layer";
 
+// Disables begin frame limiting in both cc scheduler and display scheduler.
+// Also implies --disable-gpu-vsync (see //ui/gl/gl_switches.h).
+const char kDisableFrameRateLimit[] = "disable-frame-rate-limit";
+
 base::Optional<uint32_t> GetDeadlineToSynchronizeSurfaces() {
   base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
   if (command_line->HasSwitch(switches::kRunAllCompositorStagesBeforeDraw)) {

components/viz/common/switches.h

@@ -15,12 +15,13 @@ namespace switches {
 
 // Keep list in alphabetical order.
 VIZ_COMMON_EXPORT extern const char kDeadlineToSynchronizeSurfaces[];
-VIZ_COMMON_EXPORT extern const char kDisableFrameRateLimit[];
 VIZ_COMMON_EXPORT extern const char kEnableHardwareOverlays[];
+VIZ_COMMON_EXPORT extern const char kEnableSurfaceSynchronization[];
 VIZ_COMMON_EXPORT extern const char kEnableVizDevTools[];
 VIZ_COMMON_EXPORT extern const char kEnableVizHitTestDebug[];
 VIZ_COMMON_EXPORT extern const char kRunAllCompositorStagesBeforeDraw[];
 VIZ_COMMON_EXPORT extern const char kUseVizHitTestSurfaceLayer[];
+VIZ_COMMON_EXPORT extern const char kDisableFrameRateLimit[];
 
 VIZ_COMMON_EXPORT base::Optional<uint32_t> GetDeadlineToSynchronizeSurfaces();
 

content/browser/browser_main_loop.cc

@@ -1234,6 +1234,13 @@ int BrowserMainLoop::BrowserThreadsStarted() {
   // so this cannot happen any earlier than now.
   InitializeMojo();
 
+#if BUILDFLAG(ENABLE_MUS)
+  if (features::IsUsingWindowService()) {
+    base::CommandLine::ForCurrentProcess()->AppendSwitch(
+        switches::kEnableSurfaceSynchronization);
+  }
+#endif
+
   HistogramSynchronizer::GetInstance();
 
   // cc assumes a single client name for metrics in a process, which is

content/browser/renderer_host/render_process_host_impl.cc

@@ -3064,6 +3064,7 @@ void RenderProcessHostImpl::PropagateBrowserCommandLineToRenderer(
     cc::switches::kSlowDownRasterScaleFactor,
     cc::switches::kBrowserControlsHideThreshold,
     cc::switches::kBrowserControlsShowThreshold,
+    switches::kEnableSurfaceSynchronization,
     switches::kRunAllCompositorStagesBeforeDraw,
     switches::kUseVizHitTestSurfaceLayer,
 

headless/app/headless_shell.cc

@@ -650,6 +650,7 @@ int HeadlessShellMain(int argc, const char** argv) {
     // Compositor flags
     command_line.AppendSwitch(::switches::kRunAllCompositorStagesBeforeDraw);
     command_line.AppendSwitch(::switches::kDisableNewContentRenderingTimeout);
+    command_line.AppendSwitch(::switches::kEnableSurfaceSynchronization);
     // Ensure that image animations don't resync their animation timestamps when
     // looping back around.
     command_line.AppendSwitch(::switches::kDisableImageAnimationResync);