[CrOS Tether] Do not perform host scans while the device is locked.

EasyUnlock tries to create Bluetooth connections at the lock screen, and
when both Instant Tethering and EasyUnlock try to create a Bluetooth
connection to the same device at the same time, they can cause
instability. By eliminating the possibility of this conflict, we work
around this issue.

Note that a full-fledged fix for this problem is in the works; see
https://crbug.com/752273.

Bug: 839522
Change-Id: I468515579ca46cabf279e11531ca489a71eb3255
Reviewed-on: https://chromium-review.googlesource.com/1045254
Commit-Queue: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: James Hawkins <jhawkins@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556282}

chromeos/components/tether/host_scan_scheduler_impl.cc

@@ -86,7 +86,7 @@ HostScanSchedulerImpl::~HostScanSchedulerImpl() {
 }
 
 void HostScanSchedulerImpl::ScheduleScan() {
-  EnsureScan();
+  AttemptScan();
 }
 
 void HostScanSchedulerImpl::DefaultNetworkChanged(const NetworkState* network) {
@@ -102,12 +102,12 @@ void HostScanSchedulerImpl::DefaultNetworkChanged(const NetworkState* network) {
   // NetworkStateHandlerObservers are finished running. Processing the
   // network change immediately can cause crashes; see https://crbug.com/800370.
   task_runner_->PostTask(FROM_HERE,
-                         base::BindOnce(&HostScanSchedulerImpl::EnsureScan,
+                         base::BindOnce(&HostScanSchedulerImpl::AttemptScan,
                                         weak_ptr_factory_.GetWeakPtr()));
 }
 
 void HostScanSchedulerImpl::ScanRequested() {
-  EnsureScan();
+  AttemptScan();
 }
 
 void HostScanSchedulerImpl::ScanFinished() {
@@ -142,7 +142,7 @@ void HostScanSchedulerImpl::OnSessionStateChanged() {
   delay_scan_after_unlock_timer_->Start(
       FROM_HERE,
       base::TimeDelta::FromSeconds(kNumSecondsToDelayScanAfterUnlock),
-      base::Bind(&HostScanSchedulerImpl::EnsureScan,
+      base::Bind(&HostScanSchedulerImpl::AttemptScan,
                  weak_ptr_factory_.GetWeakPtr()));
 }
 
@@ -158,10 +158,18 @@ void HostScanSchedulerImpl::SetTestDoubles(
   task_runner_ = test_task_runner;
 }
 
-void HostScanSchedulerImpl::EnsureScan() {
+void HostScanSchedulerImpl::AttemptScan() {
+  // If already scanning, there is nothing to do.
   if (host_scanner_->IsScanActive())
     return;
 
+  // If the screen is locked, a host scan should not occur.  A scan during the
+  // lock screen could cause bad interactions with EasyUnlock. See
+  // https://crbug.com/763604.
+  // Note: Once the SecureChannel API is available, this check can be removed.
+  if (session_manager_->IsScreenLocked())
+    return;
+
   // If the timer is running, this new scan is part of the same batch as the
   // previous scan, so the timer should be stopped (it will be restarted after
   // the new scan finishes). If the timer is not running, the new scan is part

chromeos/components/tether/host_scan_scheduler_impl.h

@@ -63,7 +63,7 @@ class HostScanSchedulerImpl : public HostScanScheduler,
  private:
   friend class HostScanSchedulerImplTest;
 
-  void EnsureScan();
+  void AttemptScan();
   bool IsTetherNetworkConnectingOrConnected();
   void LogHostScanBatchMetric();
 

chromeos/components/tether/host_scan_scheduler_impl_unittest.cc

@@ -191,12 +191,18 @@ TEST_F(HostScanSchedulerImplTest, ScheduleScan) {
   VerifyScanDuration(5u /* expected_num_sections */);
 }
 
-TEST_F(HostScanSchedulerImplTest, ScansWhenDeviceUnlocked) {
+TEST_F(HostScanSchedulerImplTest, TestDeviceLockAndUnlock) {
   // Lock the screen. This should not trigger a scan.
   SetScreenLockedState(true /* is_locked */);
   EXPECT_EQ(0u, fake_host_scanner_->num_scans_started());
   EXPECT_FALSE(mock_delay_scan_after_unlock_timer_->IsRunning());
 
+  // Try to start a scan. Because the screen is locked, this should not actually
+  // cause a scan to be started.
+  host_scan_scheduler_->ScheduleScan();
+  EXPECT_EQ(0u, fake_host_scanner_->num_scans_started());
+  EXPECT_FALSE(mock_delay_scan_after_unlock_timer_->IsRunning());
+
   // Unlock the screen. A scan should not yet have been started, but the timer
   // should have.
   SetScreenLockedState(false /* is_locked */);