Replace DCHECK() upon unexpected x11 event time with a workaround

ui/events/x/events_x_utils.cc

Index: ui/events/x/events_x_utils.cc
diff --git a/ui/events/x/events_x_utils.cc b/ui/events/x/events_x_utils.cc
index aab272373068313cf5ae95cd5fbb27b34fa12287..b7685f19f40fa6dcd2a3670d2b51bed20acd21a4 100644
--- a/ui/events/x/events_x_utils.cc
+++ b/ui/events/x/events_x_utils.cc
@@ -17,12 +17,14 @@
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/memory/singleton.h"
+#include "base/metrics/histogram_macros.h"
 #include "build/build_config.h"
 #include "ui/display/display.h"
 #include "ui/display/screen.h"
 #include "ui/events/devices/x11/device_data_manager_x11.h"
 #include "ui/events/devices/x11/device_list_cache_x11.h"
 #include "ui/events/devices/x11/touch_factory_x11.h"
+#include "ui/events/event_utils.h"
 #include "ui/events/keycodes/keyboard_code_conversion_x.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/geometry/rect.h"
@@ -306,12 +308,20 @@ bool GetGestureTimes(const XEvent& xev, double* start_time, double* end_time) {
   return true;
 }
 
+namespace {
 int64_t g_last_seen_timestamp_ms = 0;
-// accumulated rollover time.
 int64_t g_rollover_ms = 0;
+bool g_bogus_x11_timestamps = false;
 base::LazyInstance<std::unique_ptr<base::TickClock>>::Leaky g_tick_clock =
     LAZY_INSTANCE_INITIALIZER;
 
+enum UMAEventTimestampValidity {
+  UMA_EVENT_TIMESTAMPS_HAVE_INVALID_TIMEBASE,
+  UMA_EVENT_TIMESTAMPS_HAVE_VALID_TIMEBASE
+};
+
+}  // namespace
+
 // Takes Xlib Time and returns a time delta that is immune to timer rollover.
 // This function is not thread safe as we do not use a lock.
 base::TimeDelta TimeDeltaFromXEventTime(Time timestamp) {
@@ -320,6 +330,9 @@ base::TimeDelta TimeDeltaFromXEventTime(Time timestamp) {
   if (!timestamp)
     return base::TimeDelta();
 
+  if (g_bogus_x11_timestamps)
+    return ui::EventTimeForNow();
+
   // If this is the first event that we get, assume the time stamp roll-over
   // might have happened before the process was started.
   // Register a rollover if the distance between last timestamp and current one
@@ -343,11 +356,21 @@ base::TimeDelta TimeDeltaFromXEventTime(Time timestamp) {
 
   g_rollover_ms = now_ms & ~static_cast<int64_t>(UINT32_MAX);
   uint32_t delta = static_cast<uint32_t>(now_ms - timestamp);
-  // If using a mock clock, all bets are off -- in some tests, actual X11 events
-  // come through with real timestamps.
-  DCHECK(delta < 60 * 1000 || g_tick_clock.Get() != nullptr)
-      << "Unexpected X11 event time, now: " << now_ticks
-      << " event at: " << timestamp;
+  if (!g_tick_clock.Get()) {
+    if (delta > 60 * 1000) {
+      // x11 timestamps don't seem to be using the same time base as TimeTicks,
+      // so ignore them altogether and always use current time instead.
+      delta = 0;
+      g_bogus_x11_timestamps = true;
+      LOG(WARNING)
+          << "Unexpected x11 timestamps, will use browser time instead.";
+    }
+    UMA_HISTOGRAM_BOOLEAN("Event.TimestampHasValidTimebase",
+                          g_bogus_x11_timestamps
+                              ? UMA_EVENT_TIMESTAMPS_HAVE_INVALID_TIMEBASE
+                              : UMA_EVENT_TIMESTAMPS_HAVE_VALID_TIMEBASE);

[Ilya Sherman, 2016/05/23 18:36:33]

nit: No need to use an enum in the C++ code -- you can just log a boolean value
here.  In my previous comment, I was just asking you to update histograms.xml to
provide labels for users viewing the dashboard :)

+  }
+
   return base::TimeDelta::FromMilliseconds(now_ms - delta);
 }
 
@@ -813,6 +836,7 @@ void ResetTimestampRolloverCountersForTesting(
     std::unique_ptr<base::TickClock> tick_clock) {
   g_last_seen_timestamp_ms = 0;
   g_rollover_ms = 0;
+  g_bogus_x11_timestamps = false;
   g_tick_clock.Get() = std::move(tick_clock);
 }