If location services are turned off, have the BT chooser prompt the user to turn them on.

chrome/android/java/src/org/chromium/chrome/browser/BluetoothChooserDialog.java

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.chrome.browser;
 
 import android.Manifest;
 import android.app.Activity;
+import android.content.BroadcastReceiver;
 import android.content.Context;
 import android.content.Intent;
-import android.content.pm.PackageManager;
+import android.content.IntentFilter;
+import android.location.LocationManager;
 import android.text.SpannableString;
 import android.text.TextUtils;
 import android.view.View;
 
 import org.chromium.base.VisibleForTesting;
 import org.chromium.base.annotations.CalledByNative;
 import org.chromium.chrome.R;
 import org.chromium.chrome.browser.omnibox.OmniboxUrlEmphasizer;
 import org.chromium.chrome.browser.profiles.Profile;
 import org.chromium.components.location.LocationUtils;
 import org.chromium.ui.base.WindowAndroid;
 import org.chromium.ui.text.NoUnderlineClickableSpan;
 import org.chromium.ui.text.SpanApplier;
 import org.chromium.ui.text.SpanApplier.SpanInfo;
 
 /**
  * A dialog for picking available Bluetooth devices. This dialog is shown when a website requests to
  * pair with a certain class of Bluetooth devices (e.g. through a bluetooth.requestDevice Javascript
  * call).
+ *
+ * The dialog is shown by create() or show(), and always runs finishDialog() as it's closing.
  */
 public class BluetoothChooserDialog
         implements ItemChooserDialog.ItemSelectedCallback, WindowAndroid.PermissionCallback {
     // These constants match BluetoothChooserAndroid::ShowDiscoveryState, and are used in
     // notifyDiscoveryState().
     static final int DISCOVERY_FAILED_TO_START = 0;
     static final int DISCOVERING = 1;
     static final int DISCOVERY_IDLE = 2;
 
     // Values passed to nativeOnDialogFinished:eventType, and only used in the native function.
@@ skipping 20 matching lines @@
 
     // A pointer back to the native part of the implementation for this dialog.
     long mNativeBluetoothChooserDialogPtr;
 
     // The type of link that is shown within the dialog.
     private enum LinkType {
         EXPLAIN_BLUETOOTH,
         ADAPTER_OFF,
         ADAPTER_OFF_HELP,
         REQUEST_LOCATION_PERMISSION,
+        REQUEST_LOCATION_SERVICES,
         NEED_LOCATION_PERMISSION_HELP,
         RESTART_SEARCH,
     }
 
     /**
      * Creates the BluetoothChooserDialog.
      */
     @VisibleForTesting
     BluetoothChooserDialog(WindowAndroid windowAndroid, String origin, int securityLevel,
             long nativeBluetoothChooserDialogPtr) {
@@ skipping 42 matching lines @@
                 mActivity.getString(R.string.bluetooth_not_seeing_it_idle_some_found),
                 new SpanInfo("<link1>", "</link1>",
                         new BluetoothClickableSpan(LinkType.EXPLAIN_BLUETOOTH, mActivity)),
                 new SpanInfo("<link2>", "</link2>",
                         new BluetoothClickableSpan(LinkType.RESTART_SEARCH, mActivity)));
 
         ItemChooserDialog.ItemChooserLabels labels =
                 new ItemChooserDialog.ItemChooserLabels(title, searching, noneFound,
                         statusIdleNoneFound, statusIdleSomeFound, positiveButton);
         mItemChooserDialog = new ItemChooserDialog(mActivity, this, labels);
+
+        mActivity.registerReceiver(mLocationModeBroadcastReceiver,
+                new IntentFilter(LocationManager.MODE_CHANGED_ACTION));

[Ted C, 2016/07/01 20:18:34]

does this give a lint warning?  MODE_CHANGED_ACTION is Api 19 and I don't see
any TargetApi annotations about it

[ortuno, 2016/07/01 22:08:50]

Hmm no lint errors. Is there anything I should do about it?

[Ted C, 2016/07/01 22:22:56]

While we lack the bluetooth permission prior to M, is there anything that
prevents this code from running prior to API 19?

Since this is in the Chrome package, we don't need to be overly cautious but if
this were below content/ then we'd probably want to ensure developers of a
consistent behavior (where prior to 19 this wouldn't actually ever be called).

For now, if there are no lint errors then I guess you're fine?

+    }
+
+    // Called to report the dialog's results back to native code.
+    private void finishDialog(int resultCode, String id) {
+        mActivity.unregisterReceiver(mLocationModeBroadcastReceiver);
+        if (mNativeBluetoothChooserDialogPtr != 0) {
+            nativeOnDialogFinished(mNativeBluetoothChooserDialogPtr, resultCode, id);
+        }
     }
 
     @Override
     public void onItemSelected(String id) {
-        if (mNativeBluetoothChooserDialogPtr != 0) {
-            if (id.isEmpty()) {
-                nativeOnDialogFinished(
-                        mNativeBluetoothChooserDialogPtr, DIALOG_FINISHED_CANCELLED, "");
-            } else {
-                nativeOnDialogFinished(
-                        mNativeBluetoothChooserDialogPtr, DIALOG_FINISHED_SELECTED, id);
-            }
+        if (id.isEmpty()) {
+            finishDialog(DIALOG_FINISHED_CANCELLED, "");
+        } else {
+            finishDialog(DIALOG_FINISHED_SELECTED, id);
         }
     }
 
     @Override
     public void onRequestPermissionsResult(String[] permissions, int[] grantResults) {
-        for (int i = 0; i < grantResults.length; i++) {
+        for (int i = 0; i < permissions.length; i++) {
             if (permissions[i].equals(Manifest.permission.ACCESS_COARSE_LOCATION)) {
-                if (grantResults[i] == PackageManager.PERMISSION_GRANTED) {
+                if (checkLocationServicesAndPermission()) {
                     mItemChooserDialog.clear();
                     nativeRestartSearch(mNativeBluetoothChooserDialogPtr);
-                } else {
-                    checkLocationPermission();
                 }
                 return;
             }
         }
         // If the location permission is not present, leave the currently-shown message in place.
     }
 
-    private void checkLocationPermission() {
-        if (LocationUtils.getInstance().hasAndroidLocationPermission(mActivity)) {
-            return;
+    @VisibleForTesting
+    final BroadcastReceiver mLocationModeBroadcastReceiver = new BroadcastReceiver() {

[Ted C, 2016/07/01 20:18:34]

move this up to be with the other params (but at the bottom of them)

[ortuno, 2016/07/01 22:08:50]

Done.

+        @Override
+        public void onReceive(Context context, Intent intent) {
+            if (LocationManager.MODE_CHANGED_ACTION.equals(intent.getAction())) {

[Ted C, 2016/07/01 20:18:34]

make this an early return to avoid indenting

[ortuno, 2016/07/01 22:08:50]

Done.

+                if (checkLocationServicesAndPermission()) {
+                    mItemChooserDialog.clear();
+                    nativeRestartSearch(mNativeBluetoothChooserDialogPtr);
+                }
+            }
+        }
+    };
+
+    // Returns true if Location Services is on and Chrome has permission to see the user's location.
+    private boolean checkLocationServicesAndPermission() {
+        final boolean havePermission =
+                LocationUtils.getInstance().hasAndroidLocationPermission(mActivity);
+        final boolean locationServicesOn =
+                LocationUtils.getInstance().isSystemLocationSettingEnabled(mActivity);
+
+        if (!havePermission
+                && !mWindowAndroid.canRequestPermission(
+                           Manifest.permission.ACCESS_COARSE_LOCATION)) {
+            // Immediately close the dialog because the user has asked Chrome not to request the
+            // location permission.
+            finishDialog(DIALOG_FINISHED_DENIED_PERMISSION, "");
+            return false;
         }
 
-        if (!mWindowAndroid.canRequestPermission(Manifest.permission.ACCESS_COARSE_LOCATION)) {
-            if (mNativeBluetoothChooserDialogPtr != 0) {
-                nativeOnDialogFinished(
-                        mNativeBluetoothChooserDialogPtr, DIALOG_FINISHED_DENIED_PERMISSION, "");
-                return;
+        // Compute the message to show the user.
+        final SpanInfo permissionSpan = new SpanInfo("<permission_link>", "</permission_link>",
+                new BluetoothClickableSpan(LinkType.REQUEST_LOCATION_PERMISSION, mActivity));
+        final SpanInfo servicesSpan = new SpanInfo("<services_link>", "</services_link>",
+                new BluetoothClickableSpan(LinkType.REQUEST_LOCATION_SERVICES, mActivity));
+        final SpannableString needLocationMessage;
+        if (havePermission) {
+            if (locationServicesOn) {
+                // We don't need to request anything.
+                return true;
+            } else {
+                needLocationMessage = SpanApplier.applySpans(
+                        mActivity.getString(R.string.bluetooth_need_location_services_on),
+                        servicesSpan);
+            }
+        } else {
+            if (locationServicesOn) {
+                needLocationMessage = SpanApplier.applySpans(
+                        mActivity.getString(R.string.bluetooth_need_location_permission),
+                        permissionSpan);
+            } else {
+                needLocationMessage = SpanApplier.applySpans(
+                        mActivity.getString(
+                                R.string.bluetooth_need_location_permission_and_services_on),
+                        permissionSpan, servicesSpan);
             }
         }
 
-        SpannableString needLocationMessage = SpanApplier.applySpans(
-                mActivity.getString(R.string.bluetooth_need_location_permission),
-                new SpanInfo("<link>", "</link>",
-                        new BluetoothClickableSpan(
-                                     LinkType.REQUEST_LOCATION_PERMISSION, mActivity)));
-
         SpannableString needLocationStatus = SpanApplier.applySpans(
                 mActivity.getString(R.string.bluetooth_need_location_permission_help),
                 new SpanInfo("<link>", "</link>",
                         new BluetoothClickableSpan(
                                      LinkType.NEED_LOCATION_PERMISSION_HELP, mActivity)));
 
         mItemChooserDialog.setErrorState(needLocationMessage, needLocationStatus);
+        return false;
     }
 
     private class BluetoothClickableSpan extends NoUnderlineClickableSpan {
         // The type of link this span represents.
         private LinkType mLinkType;
 
         private Context mContext;
 
         BluetoothClickableSpan(LinkType linkType, Context context) {
             mLinkType = linkType;
@@ skipping 26 matching lines @@
                     nativeShowBluetoothAdapterOffLink(mNativeBluetoothChooserDialogPtr);
                     closeDialog();
                     break;
                 }
                 case REQUEST_LOCATION_PERMISSION: {
                     mWindowAndroid.requestPermissions(
                             new String[] {Manifest.permission.ACCESS_COARSE_LOCATION},
                             BluetoothChooserDialog.this);
                     break;
                 }
+                case REQUEST_LOCATION_SERVICES: {
+                    mContext.startActivity(
+                            LocationUtils.getInstance().getSystemLocationSettingsIntent());
+                    break;
+                }
                 case NEED_LOCATION_PERMISSION_HELP: {
                     nativeShowNeedLocationPermissionLink(mNativeBluetoothChooserDialogPtr);
                     closeDialog();
                     break;
                 }
                 case RESTART_SEARCH: {
                     mItemChooserDialog.clear();
                     nativeRestartSearch(mNativeBluetoothChooserDialogPtr);
                     break;
                 }
@@ skipping 61 matching lines @@
     @CalledByNative
     private void notifyAdapterTurnedOn() {
         mItemChooserDialog.clear();
     }
 
     @VisibleForTesting
     @CalledByNative
     void notifyDiscoveryState(int discoveryState) {
         switch (discoveryState) {
             case DISCOVERY_FAILED_TO_START: {
-                // FAILED_TO_START might be caused by a missing Location permission.
+                // FAILED_TO_START might be caused by a missing Location
+                // permission or by the Location service being turned off.
                 // Check, and show a request if so.
-                checkLocationPermission();
+                checkLocationServicesAndPermission();
                 break;
             }
             case DISCOVERY_IDLE: {
                 mItemChooserDialog.setIdleState();
                 break;
             }
             default: {
                 // TODO(jyasskin): Report the new state to the user.
                 break;
             }
         }
     }
 
     @VisibleForTesting
     native void nativeOnDialogFinished(
             long nativeBluetoothChooserAndroid, int eventType, String deviceId);
     @VisibleForTesting
     native void nativeRestartSearch(long nativeBluetoothChooserAndroid);
     // Help links.
     @VisibleForTesting
     native void nativeShowBluetoothOverviewLink(long nativeBluetoothChooserAndroid);
     @VisibleForTesting
     native void nativeShowBluetoothAdapterOffLink(long nativeBluetoothChooserAndroid);
     @VisibleForTesting
     native void nativeShowNeedLocationPermissionLink(long nativeBluetoothChooserAndroid);
 }