Add UMA histograms for the inter-process TimeTicks skew.

content/browser/frame_host/render_frame_host_impl.cc

Index: content/browser/frame_host/render_frame_host_impl.cc
diff --git a/content/browser/frame_host/render_frame_host_impl.cc b/content/browser/frame_host/render_frame_host_impl.cc
index 832911c8a939a52ce1c050de11a8a4d2675b3586..62e5538b4eecc20d8142f72c85ee019ba09a8dd9 100644
--- a/content/browser/frame_host/render_frame_host_impl.cc
+++ b/content/browser/frame_host/render_frame_host_impl.cc
@@ -7,6 +7,7 @@
 #include "base/bind.h"
 #include "base/containers/hash_tables.h"
 #include "base/lazy_instance.h"
+#include "base/metrics/histogram.h"
 #include "base/metrics/user_metrics_action.h"
 #include "base/time/time.h"
 #include "content/browser/accessibility/accessibility_mode_helper.h"
@@ -748,6 +749,23 @@ void RenderFrameHostImpl::OnBeforeUnloadACK(
         converter.ToLocalTimeTicks(
             RemoteTimeTicks::FromTimeTicks(renderer_before_unload_end_time));
     before_unload_end_time = browser_before_unload_end_time.ToTimeTicks();
+
+    // Collect UMA on the inter-process skew.
+    if (converter.IsSkewAdditiveForMetrics()) {
+      UMA_HISTOGRAM_BOOLEAN(
+          "InterProcessTimeTicks.IsSkewAdditive_RendererToBrowser", true);
+      base::TimeDelta skew = converter.GetSkewForMetrics();
+      if (skew >= base::TimeDelta()) {
+        UMA_HISTOGRAM_TIMES(
+            "InterProcessTimeTicks.BrowserBehind_RendererToBrowser", skew);
+      } else {
+        UMA_HISTOGRAM_TIMES(
+            "InterProcessTimeTicks.BrowserAhead_RendererToBrowser", -skew);
+      }
+    } else {
+      UMA_HISTOGRAM_BOOLEAN(
+          "InterProcessTimeTicks.IsSkewAdditive_RendererToBrowser", false);
+    }
   }
   frame_tree_node_->render_manager()->OnBeforeUnloadACK(
       render_view_host_->unload_ack_is_for_cross_site_transition_, proceed,