Add base::feature that injects 1ms latency to drawAndSwap

Bug: 1494868
Change-Id: I14dd10dd627f661ca34b2f14ba887a96049754ec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5016468
Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1222961}

android_webview/browser/gfx/hardware_renderer.cc

@@ -61,6 +61,9 @@ namespace {
 BASE_FEATURE(kWebViewUseOutputSurfaceClipRect,
              "WebViewUseOutputSurfaceClipRect",
              base::FEATURE_ENABLED_BY_DEFAULT);
+BASE_FEATURE(kDrawAndSwapInjectLatency,
+             "DrawAndSwapInjectLatency",
+             base::FEATURE_DISABLED_BY_DEFAULT);
 
 class ScopedAcquireExternalContext {
  public:
@@ -633,6 +636,10 @@ void HardwareRenderer::DrawAndSwap(const HardwareRendererDrawParams& params,
 
   DCHECK_CALLED_ON_VALID_THREAD(render_thread_checker_);
 
+  if (base::FeatureList::IsEnabled(kDrawAndSwapInjectLatency)) {
+    usleep(1000);
+  }
+
   // Ensure that the context is synced from external and synced back before
   // returning. This is only necessary when using ANGLE to keep its internals
   // synced with the external context