WebView: Grant sensor permission requests

Commit b6c4e590 ("Grant generic sensor permission for Android WebView")
started always granting sensors permission requests in
GetPermissionStatus().

However, commit 94c082d4 ("[sensors] Add sensors usage indicator") caused
SensorProviderProxyImpl to query PermissionManager via RequestPermission()
before making a given sensor available.

The Android WebView case was overlooked, and its RequestPermission()
implementation was still denying all requests for sensors. Update the policy
to always-grant, and while at it make CancelPermissionRequest() not show a
"not implemented" error for sensor requests, as the requests are always
granted anyway.

Doing so re-allows the WebView to provide device motion/orientation data to
users, while SensorProviderImpl::GetSensor() still prevents other types of
sensors from being accessed, just like before.

Bug: 852543
Change-Id: I3bd45f955f8ff9dca67b7b9bda940590dce258f1
Reviewed-on: https://chromium-review.googlesource.com/1104417Reviewed-by: Tao Bai <michaelbai@chromium.org>
Reviewed-by: Jun Cai <juncai@chromium.org>
Commit-Queue: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Cr-Commit-Position: refs/heads/master@{#568068}

android_webview/browser/aw_permission_manager.cc

@@ -322,7 +322,6 @@ int AwPermissionManager::RequestPermissions(
       case PermissionType::NOTIFICATIONS:
       case PermissionType::DURABLE_STORAGE:
       case PermissionType::BACKGROUND_SYNC:
-      case PermissionType::SENSORS:
       case PermissionType::FLASH:
       case PermissionType::ACCESSIBILITY_EVENTS:
       case PermissionType::CLIPBOARD_READ:
@@ -334,6 +333,11 @@ int AwPermissionManager::RequestPermissions(
                                                  PermissionStatus::DENIED);
         break;
       case PermissionType::MIDI:
+      case PermissionType::SENSORS:
+        // PermissionType::SENSORS requests are always granted so that access
+        // to device motion and device orientation data (and underlying
+        // sensors) works in the WebView. SensorProviderImpl::GetSensor()
+        // filters requests for other types of sensors.
         pending_request_raw->SetPermissionStatus(permissions[i],
                                                  PermissionStatus::GRANTED);
         break;
@@ -509,7 +513,6 @@ void AwPermissionManager::CancelPermissionRequest(int request_id) {
       case PermissionType::AUDIO_CAPTURE:
       case PermissionType::VIDEO_CAPTURE:
       case PermissionType::BACKGROUND_SYNC:
-      case PermissionType::SENSORS:
       case PermissionType::FLASH:
       case PermissionType::ACCESSIBILITY_EVENTS:
       case PermissionType::CLIPBOARD_READ:
@@ -519,6 +522,7 @@ void AwPermissionManager::CancelPermissionRequest(int request_id) {
                          << static_cast<int>(permission);
         break;
       case PermissionType::MIDI:
+      case PermissionType::SENSORS:
         // There is nothing to cancel so this is simply ignored.
         break;
       case PermissionType::NUM: