Add RemoteGATTDescriptor to WebBluetoothFunction histogram enum.

content/browser/bluetooth/bluetooth_metrics.cc

Index: content/browser/bluetooth/bluetooth_metrics.cc
diff --git a/content/browser/bluetooth/bluetooth_metrics.cc b/content/browser/bluetooth/bluetooth_metrics.cc
index d9ae54fb1e2d656fc417fd78a4d1df114bbbc8e1..579763197d21b0068d07cc5167d9e6aed1a54da4 100644
--- a/content/browser/bluetooth/bluetooth_metrics.cc
+++ b/content/browser/bluetooth/bluetooth_metrics.cc
@@ -266,6 +266,63 @@ void RecordGetCharacteristicsCharacteristic(
   }
 }
 
+void RecordGetDescriptorsDescriptor(
+    blink::mojom::WebBluetoothGATTQueryQuantity quantity,
+    const base::Optional<BluetoothUUID>& descriptor) {
+  switch (quantity) {
+    case blink::mojom::WebBluetoothGATTQueryQuantity::SINGLE:
+      UMA_HISTOGRAM_SPARSE_SLOWLY("Bluetooth.Web.GetDescriptor.Descriptor",
+                                  HashUUID(descriptor));
+      return;
+    case blink::mojom::WebBluetoothGATTQueryQuantity::MULTIPLE:
+      UMA_HISTOGRAM_SPARSE_SLOWLY("Bluetooth.Web.GetDescriptors.Descriptor",
+                                  HashUUID(descriptor));

[Ilya Sherman, 2017/02/11 00:18:27]

Are the UUIDs whitelisted in any way?  If not, is there anything that
guarantees, or at least makes likely, that this histogram will have a reasonable
number of buckets in use?

[dougt, 2017/02/11 00:56:09]

I do not think so.  The UUIDs can be any value but there are standard values
people tend to use as defined by
https://www.bluetooth.com/specifications/gatt/descriptors

[Ilya Sherman, 2017/02/11 01:02:36]

I'm not comfortable with recording a histogram that might have thousands of
buckets on any given day -- that gets very expensive in terms of computation. 
Is there a way to gather the data that you need, while providing some (expected)
limits on the number of buckets that are spanned?

[ortuno, 2017/02/13 00:34:15]

Making custom descriptors is quite rare and there are only 15 standard ones.
Furthermore interacting with descriptors is very uncommon; I would be surprised
if the number of buckets ever gets above the tens.

[Ilya Sherman, 2017/02/13 22:06:57]

Okay, thanks for clarifying that.  LGTM assuming that the number of buckets seen
in practice will be quite small.

+      return;
+  }
+}
+
+void RecordGetDescriptorsOutcome(
+    blink::mojom::WebBluetoothGATTQueryQuantity quantity,
+    UMAGetDescriptorOutcome outcome) {
+  switch (quantity) {
+    case blink::mojom::WebBluetoothGATTQueryQuantity::SINGLE:
+      UMA_HISTOGRAM_ENUMERATION(
+          "Bluetooth.Web.GetDescriptor.Outcome", static_cast<int>(outcome),
+          static_cast<int>(UMAGetDescriptorOutcome::COUNT));
+      return;
+    case blink::mojom::WebBluetoothGATTQueryQuantity::MULTIPLE:
+      UMA_HISTOGRAM_ENUMERATION(
+          "Bluetooth.Web.GetDescriptors.Outcome", static_cast<int>(outcome),
+          static_cast<int>(UMAGetDescriptorOutcome::COUNT));
+      return;
+  }
+}
+
+void RecordGetDescriptorsOutcome(
+    blink::mojom::WebBluetoothGATTQueryQuantity quantity,
+    CacheQueryOutcome outcome) {
+  switch (outcome) {
+    case CacheQueryOutcome::SUCCESS:
+    case CacheQueryOutcome::BAD_RENDERER:
+      // No need to record a success or renderer crash.
+      NOTREACHED();
+      return;
+    case CacheQueryOutcome::NO_DEVICE:
+      RecordGetDescriptorsOutcome(quantity, UMAGetDescriptorOutcome::NO_DEVICE);
+      return;
+    case CacheQueryOutcome::NO_SERVICE:
+      RecordGetDescriptorsOutcome(quantity,
+                                  UMAGetDescriptorOutcome::NO_SERVICE);
+      return;
+    case CacheQueryOutcome::NO_CHARACTERISTIC:
+      RecordGetDescriptorsOutcome(quantity,
+                                  UMAGetDescriptorOutcome::NO_CHARACTERISTIC);
+    case CacheQueryOutcome::NO_DESCRIPTOR:
+      NOTREACHED();
+      return;
+  }
+}
+
 // GATT Operations
 
 void RecordGATTOperationOutcome(UMAGATTOperation operation,