Add UMA metrics for internal display zoom factor changes

This patch records UMA metrics for any change to the internal display's
zoom factor. It does not record temporary zoom factor changes by
debouncing signals that are within a small interval and only allowing
the last signal to pass through.

Bug: 849894
Change-Id: I2dc7d31e9910855ca4a59834a56d8322641a9f5b
Component: Display Manager, UMA, Zoom
Reviewed-on: https://chromium-review.googlesource.com/1093270Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Malay Keshav <malaykeshav@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567855}

tools/metrics/histograms/histograms.xml

@@ -17818,6 +17818,15 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="DisplayManager.InternalDisplayZoomPercentage" units="%">
+  <owner>malaykeshav@chromium.org</owner>
+  <summary>
+    The zoom percentage that the user has set on the internal display and is
+    actively using. This is emitted when the zoom factor has been updated in
+    display manager and has not been changed for a while.
+  </summary>
+</histogram>
+
 <histogram name="DisplayManager.MirroringDisplayCountRanges"
     enum="MultiDisplayModeDisplayCountRanges">
   <owner>weidongg@chromium.org</owner>

ui/display/manager/display_manager.cc

@@ -40,6 +40,7 @@
 
 #if defined(OS_CHROMEOS)
 #include "base/sys_info.h"
+#include "base/time/time.h"
 #include "chromeos/system/devicemode.h"
 #include "ui/display/manager/display_util.h"
 #endif
@@ -64,6 +65,17 @@ const char kMirrorModeTypesHistogram[] = "DisplayManager.MirrorModeTypes";
 const char kMirroringDisplayCountRangesHistogram[] =
     "DisplayManager.MirroringDisplayCountRanges";
 
+#if defined(OS_CHROMEOS)
+// The UMA historgram that logs the zoom percentage level of the intenral
+// display.
+constexpr char kInternalDisplayZoomPercentageHistogram[] =
+    "DisplayManager.InternalDisplayZoomPercentage";
+
+// Timeout in seconds after which we consider the change to the display zoom
+// is not temporary.
+constexpr int kDisplayZoomModifyTimeoutSec = 15;
+#endif  // defined(OS_CHROMEOS)
+
 struct DisplaySortFunctor {
   bool operator()(const Display& a, const Display& b) {
     return CompareDisplayIds(a.id(), b.id());
@@ -305,6 +317,19 @@ enum class MirrorModeTypes {
   kCount,
 };
 
+#if defined(OS_CHROMEOS)
+void OnInternalDisplayZoomChanged(float zoom_factor) {
+  constexpr static int kMaxValue = 300;
+  constexpr static int kBucketSize = 5;
+  constexpr static int kNumBuckets = kMaxValue / kBucketSize + 1;
+
+  base::LinearHistogram::FactoryGet(
+      kInternalDisplayZoomPercentageHistogram, kBucketSize, kMaxValue,
+      kNumBuckets, base::HistogramBase::kUmaTargetedHistogramFlag)
+      ->Add(std::round(zoom_factor * 100));
+}
+#endif  // defined(OS_CHROMEOS)
+
 }  // namespace
 
 DisplayManager::BeginEndNotifier::BeginEndNotifier(
@@ -343,6 +368,7 @@ DisplayManager::~DisplayManager() {
 #if defined(OS_CHROMEOS)
   // Reset the font params.
   gfx::SetFontRenderParamsDeviceScaleFactor(1.0f);
+  on_display_zoom_modify_timeout_.Cancel();
 #endif
 }
 
@@ -1516,6 +1542,15 @@ void DisplayManager::UpdateZoomFactor(int64_t display_id, float zoom_factor) {
   if (iter == display_info_.end())
     return;
 
+  if (Display::IsInternalDisplayId(display_id)) {
+    on_display_zoom_modify_timeout_.Cancel();
+    on_display_zoom_modify_timeout_.Reset(
+        base::BindRepeating(&OnInternalDisplayZoomChanged, zoom_factor));
+    base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
+        FROM_HERE, on_display_zoom_modify_timeout_.callback(),
+        base::TimeDelta::FromSeconds(kDisplayZoomModifyTimeoutSec));
+  }
+
   iter->second.set_zoom_factor(zoom_factor);
 
   for (const auto& display : active_display_list_) {
@@ -1658,8 +1693,9 @@ bool DisplayManager::ZoomDisplay(int64_t display_id, bool up) {
   if (next_zoom_idx < 0 || next_zoom_idx >= zooms.size())
     return false;
 
-  iter->second.set_zoom_factor(zooms[next_zoom_idx]);
-  UpdateDisplays();
+  // Update zoom factor via the display manager API to ensure UMA metrics are
+  // recorded.
+  UpdateZoomFactor(display_id, zooms[next_zoom_idx]);
   return true;
 #else
   return false;

ui/display/manager/display_manager.h

@@ -33,6 +33,7 @@
 #include "ui/display/unified_desktop_utils.h"
 
 #if defined(OS_CHROMEOS)
+#include "base/cancelable_callback.h"
 #include "base/optional.h"
 #include "ui/display/manager/display_configurator.h"
 #include "ui/display/manager/touch_device_manager.h"
@@ -686,6 +687,13 @@ class DISPLAY_MANAGER_EXPORT DisplayManager
 
 #if defined(OS_CHROMEOS)
   std::unique_ptr<TouchDeviceManager> touch_device_manager_;
+
+  // A cancelable callback to trigger sending UMA metrics when display zoom is
+  // updated. The reason we need a cancelable callback is because we dont want
+  // to record UMA metrics for changes to the display zoom that are temporary.
+  // Temporary changes may include things like the user trying out different
+  // zoom levels before making the final decision.
+  base::CancelableCallback<void()> on_display_zoom_modify_timeout_;
 #endif
 
   // Whether mirroring across multiple displays is enabled.