Add UMA for the number of devices in the chooser when a device is paired

chrome/browser/ui/bluetooth/bluetooth_chooser_controller.cc

Index: chrome/browser/ui/bluetooth/bluetooth_chooser_controller.cc
diff --git a/chrome/browser/ui/bluetooth/bluetooth_chooser_controller.cc b/chrome/browser/ui/bluetooth/bluetooth_chooser_controller.cc
index 13f85f20d01d0b085d6feee15fb0e7b9cce38d34..08a8a3def8ef651ebff0a074c856baa2aa002746 100644
--- a/chrome/browser/ui/bluetooth/bluetooth_chooser_controller.cc
+++ b/chrome/browser/ui/bluetooth/bluetooth_chooser_controller.cc
@@ -32,15 +32,26 @@ void RecordInteractionWithChooser(bool has_null_handler) {
   UMA_HISTOGRAM_BOOLEAN("Bluetooth.Web.ChooserInteraction", has_null_handler);
 }
 
+void RecordNumOfDevices(bool accept_all_devices, size_t num_of_devices) {
+  if (accept_all_devices) {
+    UMA_HISTOGRAM_SPARSE_SLOWLY(
+        "Bluetooth.Web.RequestDevice."
+        "NumOfDevicesInChooserWhenNotAcceptingAllDevices",
+        num_of_devices);

[Ilya Sherman, 2016/12/17 01:05:45]

Please cap the value that can be recorded here to something reasonable, like
100.

[juncai, 2016/12/19 20:17:57]

Done.

+  }
+}
+
 }  // namespace
 
 BluetoothChooserController::BluetoothChooserController(
     content::RenderFrameHost* owner,
-    const content::BluetoothChooser::EventHandler& event_handler)
+    const content::BluetoothChooser::EventHandler& event_handler,
+    bool accept_all_devices)
     : ChooserController(owner,
                         IDS_BLUETOOTH_DEVICE_CHOOSER_PROMPT_ORIGIN,
                         IDS_BLUETOOTH_DEVICE_CHOOSER_PROMPT_EXTENSION_NAME),
-      event_handler_(event_handler) {}
+      event_handler_(event_handler),
+      accept_all_devices_(accept_all_devices) {}
 
 BluetoothChooserController::~BluetoothChooserController() {}
 
@@ -115,6 +126,7 @@ void BluetoothChooserController::Select(const std::vector<size_t>& indices) {
     return;
   }
   DCHECK_LT(index, devices_.size());
+  RecordNumOfDevices(accept_all_devices_, devices_.size());
   event_handler_.Run(content::BluetoothChooser::Event::SELECTED,
                      devices_[index].id);
 }