sensors: Ensure a document without an associated frame does not crash

Commit d1034e1e ("sensors: Make SensorProviderProxy supplement Document,
not LocalFrame") tied a sensor's lifetime to a document rather than a frame,
but we continued to assume Document::GetFrame() would never return null.

This is not true, as evidenced by the crash reports in bug 889754, caused by
SensorProxy::ShouldSuspendUpdates() trying to invoke methods on a LocalFrame
that can actually be a nullptr.

The original backtrace in the bug report seems to come from sensor creation,
but it is easier to trigger the same crash with a focus change after
destroying a sensor's document's frame.

Bug: 861675, 889754
Change-Id: Idb9ed5c18a655e113e2fb76cde6615aeefcc544a
Reviewed-on: https://chromium-review.googlesource.com/1256826Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Raphael Kubo da Costa (CET) <raphael.kubo.da.costa@intel.com>
Cr-Commit-Position: refs/heads/master@{#595958}

third_party/WebKit/LayoutTests/external/wpt/accelerometer/Accelerometer-iframe-access.https-expected.txt

 This is a testharness.js-based test.
 PASS Accelerometer: sensor is suspended and resumed when focus traverses from to cross-origin frame
 PASS Accelerometer: sensor is not suspended when focus traverses from to same-origin frame
+PASS Accelerometer: losing a document's frame with an active sensor does not crash
 PASS LinearAccelerationSensor: sensor is suspended and resumed when focus traverses from to cross-origin frame
 PASS LinearAccelerationSensor: sensor is not suspended when focus traverses from to same-origin frame
+PASS LinearAccelerationSensor: losing a document's frame with an active sensor does not crash
 FAIL GravitySensor: sensor is suspended and resumed when focus traverses from to cross-origin frame assert_true: expected true got false
 FAIL GravitySensor: sensor is not suspended when focus traverses from to same-origin frame assert_true: expected true got false
+FAIL GravitySensor: losing a document's frame with an active sensor does not crash assert_true: expected true got false
 Harness: the test ran to completion.
 

third_party/WebKit/LayoutTests/external/wpt/generic-sensor/generic-sensor-iframe-tests.sub.js

@@ -5,7 +5,6 @@ async function send_message_to_iframe(iframe, message, reply) {
 
   return new Promise((resolve, reject) => {
     let messageHandler = e => {
-
       if (e.data.command !== message.command) {
         return;
       }
@@ -131,4 +130,31 @@ function run_generic_sensor_iframe_tests(sensorName) {
     iframe.parentNode.removeChild(iframe);
   }, `${sensorName}: sensor is not suspended when focus traverses from\
  to same-origin frame`);
+
+  sensor_test(async t => {
+    assert_true(sensorName in self);
+    const iframe = document.createElement('iframe');
+    iframe.allow = featurePolicies.join(';') + ';';
+    iframe.src = 'https://{{host}}:{{ports[https][0]}}/generic-sensor/resources/iframe_sensor_handler.html';
+
+    // Create sensor in the iframe (we do not care whether this is a
+    // cross-origin nested context in this test).
+    const iframeLoadWatcher = new EventWatcher(t, iframe, 'load');
+    document.body.appendChild(iframe);
+    await iframeLoadWatcher.wait_for('load');
+    await send_message_to_iframe(iframe, {command: 'create_sensor',
+                                          type: sensorName});
+    iframe.contentWindow.focus();
+    await send_message_to_iframe(iframe, {command: 'start_sensor'});
+
+    // Remove iframe from main document and change focus. When focus changes,
+    // we need to determine whether a sensor must have its execution suspended
+    // or resumed (section 4.2.3, "Focused Area" of the Generic Sensor API
+    // spec). In Blink, this involves querying a frame, which might no longer
+    // exist at the time of the check.
+    // Note that we cannot send the "reset_sensor_backend" command because the
+    // iframe is discarded with the removeChild call.
+    iframe.parentNode.removeChild(iframe);
+    window.focus();
+  }, `${sensorName}: losing a document's frame with an active sensor does not crash`);
 }

third_party/WebKit/LayoutTests/external/wpt/geolocation-sensor/GeolocationSensor-iframe-access.https-expected.txt

 This is a testharness.js-based test.
 FAIL GeolocationSensor: sensor is suspended and resumed when focus traverses from to cross-origin frame assert_true: expected true got false
 FAIL GeolocationSensor: sensor is not suspended when focus traverses from to same-origin frame assert_true: expected true got false
+FAIL GeolocationSensor: losing a document's frame with an active sensor does not crash assert_true: expected true got false
 Harness: the test ran to completion.
 

third_party/WebKit/LayoutTests/external/wpt/magnetometer/Magnetometer-iframe-access.https-expected.txt

 This is a testharness.js-based test.
 PASS Magnetometer: sensor is suspended and resumed when focus traverses from to cross-origin frame
 PASS Magnetometer: sensor is not suspended when focus traverses from to same-origin frame
+PASS Magnetometer: losing a document's frame with an active sensor does not crash
 FAIL UncalibratedMagnetometer: sensor is suspended and resumed when focus traverses from to cross-origin frame assert_true: expected true got false
 FAIL UncalibratedMagnetometer: sensor is not suspended when focus traverses from to same-origin frame assert_true: expected true got false
+FAIL UncalibratedMagnetometer: losing a document's frame with an active sensor does not crash assert_true: expected true got false
 Harness: the test ran to completion.
 

third_party/blink/renderer/modules/sensor/sensor_proxy.cc

@@ -115,10 +115,11 @@ bool SensorProxy::ShouldSuspendUpdates() const {
     return true;
 
   LocalFrame* focused_frame = GetPage()->GetFocusController().FocusedFrame();
-  if (!focused_frame)
+  LocalFrame* this_frame = provider_->GetSupplementable()->GetFrame();
+
+  if (!focused_frame || !this_frame)
     return true;
 
-  LocalFrame* this_frame = provider_->GetSupplementable()->GetFrame();
   if (focused_frame == this_frame)
     return false;