Stop using [Client=...] feature of Mojom for BatteryMonitor

device/battery/battery_monitor.mojom

Index: device/battery/battery_monitor.mojom
diff --git a/device/battery/battery_monitor.mojom b/device/battery/battery_monitor.mojom
index 880685e61ca3263039827c1838d55ce742a3bf7b..88a43d287e9f1c7a576c1dba312cd38acdfbdce0 100644
--- a/device/battery/battery_monitor.mojom
+++ b/device/battery/battery_monitor.mojom
@@ -6,11 +6,10 @@ module device;
 
 import "device/battery/battery_status.mojom";
 
-// A BatteryMonitor will periodically call its client's DidChange method.
-[Client=BatteryStatusObserver]

[timvolodine, 2015/01/07 14:38:51]

does this mean the [Client=..] feature is deprecated and should not be used
anymore? the idea seemed kind of nice and resulted in simpler monitor
implementation. I understand the new design is because we care about
producer/consumer synchronization. If this is a general concern maybe there is a
way to have a mojo client primitive which would not queue and transmit only the
last data (similar to what we have with shared memory).

 interface BatteryMonitor {
-};
-
-interface BatteryStatusObserver {
-  DidChange(BatteryStatus status);
+  // Battery status is reported once it changes or immediately if this is the
+  // first call to QueryNextStatus on this instance. QueryNextStatus calls may
+  // be throttled by the service. Overlapping calls to QueryNextStatus are
+  // supported.

[timvolodine, 2015/01/07 14:38:51]

description for this patch talks about an anti-pattern issue - is there any bug
associated with this? if so maybe add it to description.

[ppi, 2015/01/07 19:37:36]

Did you mean s/supported/not supported/?

[ppi, 2015/01/07 19:41:12]

Ach, you probably did mean "supported", please disregard.

[darin (slow to review), 2015/01/07 20:39:52]

Yup, this is what the queuing of callbacks is all about in the implementation.

+  QueryNextStatus() => (BatteryStatus status);

[qsr, 2015/01/07 09:05:00]

Any reason you choose this design, instead of having something like:

  StartObserving(BatteryStatusObserver observer);

The reason I asked is because this doubled the number of message for this API =>
Until now, the monitor was sending all updates, now the client must call this
method back each time it reveives an update.

 };