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

base/power_monitor/power_monitor_device_source_mac.mm

Index: base/power_monitor/power_monitor_device_source_mac.mm
diff --git a/base/power_monitor/power_monitor_device_source_mac.mm b/base/power_monitor/power_monitor_device_source_mac.mm
index 8c48117e22007f522e6d4433ff3e1ed621fb3f31..aa7274574d51ab39a1b8c741c872651d796d8e9d 100644
--- a/base/power_monitor/power_monitor_device_source_mac.mm
+++ b/base/power_monitor/power_monitor_device_source_mac.mm
@@ -11,6 +11,8 @@
 #include "base/power_monitor/power_monitor_source.h"
 
 #include <IOKit/IOMessage.h>
+#include <IOKit/ps/IOPSKeys.h>
+#include <IOKit/ps/IOPowerSources.h>
 #include <IOKit/pwr_mgt/IOPMLib.h>
 
 namespace base {
@@ -19,6 +21,29 @@ void ProcessPowerEventHelper(PowerMonitorSource::PowerEvent event) {
   PowerMonitorSource::ProcessPowerEvent(event);
 }
 
+bool PowerMonitorDeviceSource::IsOnBatteryPowerImpl() {

[Nico, 2016/09/20 00:05:08]

how often do we poll this? there's a "this changed" observer interface on os x i
think

[DaleCurtis, 2016/09/20 00:15:13]

Doesn't look like it's called very much anywhere. It looks like media/ may be
the biggest user:
https://cs.chromium.org/search/?q=IsOnBatteryPower&type=cs&sq=package:chromium

We're calling it probably every 5 seconds. I look for another interface, but I
think the one you're talking about is used here: 
https://cs.chromium.org/chromium/src/device/battery/battery_status_manager_ma...

Even then it requires repolling all sources on any state change notification. I
guess the state change notification isn't specific enough. Unfortunately this
API also requires a run loop :/

I think I'm going to need that here after all though, since sources are supposed
to send PowerMonitorSource::POWER_STATE_EVENT when the battery status changed.

[Robert Sesek, 2016/09/20 18:19:56]

I do think we should use the IOPSNotificationCreateRunLoopSource() interface
instead. The run loop source could be installed on the main thread without
issue, and when it's received, it could bounce the IOPSCopyPowerSourcesInfo()
work onto a worker pool, and the result could then be cached.
That's my conclusion as well. It looks like the caching may be done for you,
too:
https://cs.chromium.org/chromium/src/base/power_monitor/power_monitor_source....

[DaleCurtis, 2016/09/21 22:49:39]

Done.

+  base::ScopedCFTypeRef<CFTypeRef> info(IOPSCopyPowerSourcesInfo());
+  base::ScopedCFTypeRef<CFArrayRef> power_sources_list(
+      IOPSCopyPowerSourcesList(info));
+
+  const CFIndex count = CFArrayGetCount(power_sources_list);
+  for (CFIndex i = 0; i < count; ++i) {
+    const CFDictionaryRef description = IOPSGetPowerSourceDescription(
+        info, CFArrayGetValueAtIndex(power_sources_list, i));
+    if (!description)
+      continue;
+
+    CFStringRef current_state = base::mac::GetValueFromDictionary<CFStringRef>(
+        description, CFSTR(kIOPSPowerSourceStateKey));
+
+    // We only report "on battery power" if no source is on AC power.
+    if (!CFStringsAreEqual(current_state, CFSTR(kIOPSBatteryPowerValue)))
+      return false;
+  }
+
+  return true;
+}
+
 namespace {
 
 io_connect_t g_system_power_io_port = 0;