[Bluetooth] Add security note for all blobs in device.mojom.

As per post-submission convo in crrev.com/c/2370094.

Change-Id: I1a8ab0fd4ff9bf1b27cbfe05c36408fce9bf2438
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2402399
Commit-Queue: Ryan Hansberry <hansberry@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805925}

device/bluetooth/public/mojom/device.mojom

@@ -6,6 +6,13 @@ module bluetooth.mojom;
 
 import "device/bluetooth/public/mojom/uuid.mojom";
 
+// Important note: the byte arrays which can be accessed from this interface
+// (including "service data", "characteristics", and "descriptors") are
+// arbitrary binary blobs of data provided by a likely untrustworthy device.
+// Clients are responsible for safely parsing this information; please see
+// "The Rule of 2" (//docs/security/rule-of-2.md). C++ clients must parse these
+// blobs in a sandboxed process.
+
 // Values representing the possible properties of a characteristic, which
 // define how the characteristic can be used. Each of these properties serve
 // a role as defined in the Bluetooth Specification.
@@ -61,11 +68,8 @@ struct DeviceInfo {
   bool is_gatt_connected;
   RSSIWrapper? rssi;
 
-  // Important note: the "service data" associated with each UUID is an
-  // arbitrary binary blob of data provided by a likely untrustworthy device.
-  // Clients are responsible for safely parsing this information; please see
-  // "The Rule of 2" (//docs/security/rule-of-2.md). C++ clients must parse this
-  // blob in a sandbox process.
+  // Important: the blobs associated with each UUID are arbitrary and untrusted.
+  // Please refer to the note on "The Rule of 2" at the top of this file.
   map<UUID, array<uint8>> service_data_map;
 };
 
@@ -79,12 +83,18 @@ struct CharacteristicInfo {
   string id;
   UUID uuid;
   uint32 properties;
+
+  // Important: this blob is arbitrary and untrusted. Please refer to the note
+  // on "The Rule of 2" at the top of this file.
   array<uint8> last_known_value;
 };
 
 struct DescriptorInfo {
   string id;
   UUID uuid;
+
+  // Important: this blob is arbitrary and untrusted. Please refer to the note
+  // on "The Rule of 2" at the top of this file.
   array<uint8> last_known_value;
 };
 
@@ -127,12 +137,16 @@ interface Device {
   // Reads the value for the GATT Descriptor with |descriptor_id| in the GATT
   // Characteristic with |characteristic_id| in the GATT Service with
   // |service_id|.
+  // Important: the returned |value| blob is arbitrary and untrusted. Please
+  // refer to the note on "The Rule of 2" at the top of this file.
   ReadValueForDescriptor(string service_id, string characteristic_id,
       string descriptor_id) => (GattResult result, array<uint8>? value);
 
   // Writes the |value| for the GATT Descriptor with |descriptor_id| in the GATT
   // Characteristic with |characteristic_id| in the GATT Service with
   // |service_id|.
+  // Important: the returned |value| blob is arbitrary and untrusted. Please
+  // refer to the note on "The Rule of 2" at the top of this file.
   WriteValueForDescriptor(string service_id, string characteristic_id,
       string descriptor_id, array<uint8> value) => (GattResult result);
 };