Change Gamepad.index to signed int to match spec.

This hasn't been an issue since Gamepads on the navigator array should
always have index >= 0. However, WebXR Gamepads that are not on the
navigator array must have an index of -1.

Bug: 950202
Change-Id: Ia3abd606ae491cbdc738fc7a0c8fbde9eaf57e43
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1721057Reviewed-by: Matt Reynolds <mattreynolds@chromium.org>
Reviewed-by: David Dorwin <ddorwin@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Commit-Queue: Jacob DeWitt <jacde@chromium.org>
Cr-Commit-Position: refs/heads/master@{#681885}

third_party/blink/renderer/modules/gamepad/gamepad.cc

@@ -34,7 +34,7 @@
 namespace blink {
 
 Gamepad::Gamepad(Client* client,
-                 unsigned index,
+                 int index,
                  base::TimeTicks time_origin,
                  base::TimeTicks time_floor)
     : client_(client),

third_party/blink/renderer/modules/gamepad/gamepad.h

@@ -52,7 +52,7 @@ class MODULES_EXPORT Gamepad final : public ScriptWrappable {
   };
 
   Gamepad(Client* client,
-          unsigned index,
+          int index,
           base::TimeTicks time_origin,
           base::TimeTicks time_floor);
   ~Gamepad() override;
@@ -64,7 +64,7 @@ class MODULES_EXPORT Gamepad final : public ScriptWrappable {
   const String& id() const { return id_; }
   void SetId(const String& id) { id_ = id; }
 
-  unsigned index() const { return index_; }
+  int index() const { return index_; }
 
   bool connected() const { return connected_; }
   void SetConnected(bool val) { connected_ = val; }
@@ -109,7 +109,7 @@ class MODULES_EXPORT Gamepad final : public ScriptWrappable {
   String id_;
 
   // The index of this gamepad within the GamepadList.
-  const unsigned index_;
+  const int index_;
 
   // True if this gamepad was still connected when gamepad state was captured.
   bool connected_;

third_party/blink/renderer/modules/gamepad/gamepad.idl

@@ -43,7 +43,7 @@ enum GamepadMappingType {
 // https://w3c.github.io/gamepad/#gamepad-interface
 interface Gamepad {
     readonly attribute DOMString id;
-    readonly attribute unsigned long index;
+    readonly attribute long index;
     readonly attribute boolean connected;
     readonly attribute DOMHighResTimeStamp timestamp;
     readonly attribute GamepadMappingType mapping;

third_party/blink/renderer/modules/gamepad/navigator_gamepad.cc

@@ -149,11 +149,12 @@ GamepadHapticActuator* NavigatorGamepad::GetVibrationActuatorForGamepad(
     return nullptr;
   }
 
-  uint32_t pad_index = gamepad.index();
   if (!gamepad.HasVibrationActuator()) {
     return nullptr;
   }
 
+  int pad_index = gamepad.index();
+  DCHECK_GE(pad_index, 0);
   if (!vibration_actuators_[pad_index]) {
     ExecutionContext* context =
         DomWindow() ? DomWindow()->GetExecutionContext() : nullptr;