Implement base::PowerMonitor::IsOnBatteryPower() for OSX.

base/power_monitor/power_monitor_device_source_ios.mm

Index: base/power_monitor/power_monitor_device_source_ios.mm
diff --git a/base/power_monitor/power_monitor_device_source_ios.mm b/base/power_monitor/power_monitor_device_source_ios.mm
index dc12f1c2952007200f227826c7e1ec046646dadd..3e86b2e246c5bed445e87cc374b16f9ce00a5941 100644
--- a/base/power_monitor/power_monitor_device_source_ios.mm
+++ b/base/power_monitor/power_monitor_device_source_ios.mm
@@ -8,6 +8,11 @@
 
 namespace base {
 
+bool PowerMonitorDeviceSource::IsOnBatteryPowerImpl() {

[Nico, 2016/09/27 20:19:27]

Is this used by anything on iOS? If not, maybe we can not provide an
implementation so we'll get a link error if something starts using it. If it is
used on iOS, there should probably be a bug about for implementing it.

[DaleCurtis, 2016/09/27 20:53:42]

ios_chrome_unittests fails to link without this, but I haven't found anything
using it explicitly. See any of the previous patch set try jobs for more
details. Here's the exact error w/o this for posterity:

FAILED: obj/ios/chrome/arm/ios_chrome_unittests 
...
Undefined symbols for architecture armv7:
  "base::PowerMonitorDeviceSource::IsOnBatteryPowerImpl()", referenced from:
      vtable for base::PowerMonitorDeviceSource in
libbase.a(power_monitor_device_source.o)

https://build.chromium.org/p/tryserver.chromium.mac/builders/ios-device/build...

+  NOTIMPLEMENTED();
+  return false;
+}
+
 void PowerMonitorDeviceSource::PlatformInit() {
   NSNotificationCenter* nc = [NSNotificationCenter defaultCenter];
   id foreground =