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

Index: chrome/android/java/src/org/chromium/chrome/browser/BluetoothChooserDialog.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/BluetoothChooserDialog.java b/chrome/android/java/src/org/chromium/chrome/browser/BluetoothChooserDialog.java
index df15c1638c115883800da2309259c17a7c314a7d..59f8d26b3bb7c635a59c7b62b389cc8156b221ff 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/BluetoothChooserDialog.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/BluetoothChooserDialog.java
@@ -6,9 +6,11 @@ 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;
@@ -28,6 +30,8 @@ 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 {
@@ -68,6 +72,7 @@ public class BluetoothChooserDialog
         ADAPTER_OFF,
         ADAPTER_OFF_HELP,
         REQUEST_LOCATION_PERMISSION,
+        REQUEST_LOCATION_SERVICES,
         NEED_LOCATION_PERMISSION_HELP,
         RESTART_SEARCH,
     }
@@ -130,30 +135,35 @@ public class BluetoothChooserDialog
                 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;
             }
@@ -161,24 +171,62 @@ public class BluetoothChooserDialog
         // 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);
+                }
+            }
         }
+    };
 
-        if (!mWindowAndroid.canRequestPermission(Manifest.permission.ACCESS_COARSE_LOCATION)) {
-            if (mNativeBluetoothChooserDialogPtr != 0) {
-                nativeOnDialogFinished(
-                        mNativeBluetoothChooserDialogPtr, DIALOG_FINISHED_DENIED_PERMISSION, "");
-                return;
-            }
+    // 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;
         }
 
-        SpannableString needLocationMessage = SpanApplier.applySpans(
-                mActivity.getString(R.string.bluetooth_need_location_permission),
-                new SpanInfo("<link>", "</link>",
-                        new BluetoothClickableSpan(
-                                     LinkType.REQUEST_LOCATION_PERMISSION, mActivity)));
+        // 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 needLocationStatus = SpanApplier.applySpans(
                 mActivity.getString(R.string.bluetooth_need_location_permission_help),
@@ -187,6 +235,7 @@ public class BluetoothChooserDialog
                                      LinkType.NEED_LOCATION_PERMISSION_HELP, mActivity)));
 
         mItemChooserDialog.setErrorState(needLocationMessage, needLocationStatus);
+        return false;
     }
 
     private class BluetoothClickableSpan extends NoUnderlineClickableSpan {
@@ -233,6 +282,11 @@ public class BluetoothChooserDialog
                             BluetoothChooserDialog.this);
                     break;
                 }
+                case REQUEST_LOCATION_SERVICES: {
+                    mContext.startActivity(
+                            LocationUtils.getInstance().getSystemLocationSettingsIntent());
+                    break;
+                }
                 case NEED_LOCATION_PERMISSION_HELP: {
                     nativeShowNeedLocationPermissionLink(mNativeBluetoothChooserDialogPtr);
                     closeDialog();
@@ -314,9 +368,10 @@ public class BluetoothChooserDialog
     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: {