Add a timer histogram for PalmDetectionFilter Filter time, and test it.

This adds a timer histogram for all PalmDetectionFilter->Filter
executions. We'll keep the timer whenever we change the underlying
filter implementation.

Adds a unit test that ensures the timer is populated.

Bug: 982118
Change-Id: I410ca0348bca9c556f4dff05ab5e228a1f09516d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1824796Reviewed-by: Michael Spang <spang@chromium.org>
Commit-Queue: Rob Schonberger <robsc@google.com>
Cr-Commit-Position: refs/heads/master@{#699983}

ui/events/ozone/evdev/touch_event_converter_evdev.cc

@@ -553,7 +553,10 @@ void TouchEventConverterEvdev::ReportEvents(base::TimeTicks timestamp) {
   if (false_touch_finder_)
     false_touch_finder_->HandleTouches(events_, timestamp);
   std::bitset<kNumTouchEvdevSlots> hold, suppress;
-  palm_detection_filter_->Filter(events_, timestamp, &hold, &suppress);
+  {
+    SCOPED_UMA_HISTOGRAM_TIMER(kPalmFilterTimerEventName);
+    palm_detection_filter_->Filter(events_, timestamp, &hold, &suppress);
+  }
   for (size_t i = 0; i < events_.size(); i++) {
     InProgressTouchEvdev* event = &events_[i];
     if (IsPalm(*event)) {
@@ -683,4 +686,6 @@ const char TouchEventConverterEvdev::kHoldCountAtReleaseEventName[] =
     "Ozone.TouchEventConverterEvdev.HoldCountAtRelease";
 const char TouchEventConverterEvdev::kHoldCountAtCancelEventName[] =
     "Ozone.TouchEventConverterEvdev.HoldCountAtCancel";
+const char TouchEventConverterEvdev::kPalmFilterTimerEventName[] =
+    "Ozone.TouchEventConverterEvdev.PalmDetectionFilterTime";
 }  // namespace ui

ui/events/ozone/evdev/touch_event_converter_evdev.h

@@ -70,6 +70,7 @@ class EVENTS_OZONE_EVDEV_EXPORT TouchEventConverterEvdev
 
   static const char kHoldCountAtReleaseEventName[];
   static const char kHoldCountAtCancelEventName[];
+  static const char kPalmFilterTimerEventName[];
 
  private:
   friend class MockTouchEventConverterEvdev;

ui/events/ozone/evdev/touch_event_converter_evdev_unittest.cc

@@ -1628,6 +1628,9 @@ TEST_F(TouchEventConverterEvdevTest, HeldEventNotSent) {
   EXPECT_THAT(histogram_tester_.GetAllSamples(
                   TouchEventConverterEvdev::kHoldCountAtCancelEventName),
               testing::ElementsAre());
+  EXPECT_THAT(histogram_tester_.GetAllSamples(
+                  TouchEventConverterEvdev::kPalmFilterTimerEventName),
+              testing::SizeIs(1));
 }
 
 TEST_F(TouchEventConverterEvdevTest, HeldThenEnd) {