5 files changed, 74 insertions, 25 deletions

diff --git a/device/battery/android/java/src/org/chromium/device/battery/BatteryMonitorImpl.java b/device/battery/android/java/src/org/chromium/device/battery/BatteryMonitorImpl.java
index e441589..364e21a 100644
--- a/device/battery/android/java/src/org/chromium/device/battery/BatteryMonitorImpl.java
+++ b/device/battery/android/java/src/org/chromium/device/battery/BatteryMonitorImpl.java
@@ -7,7 +7,9 @@ package org.chromium.device.battery;
 import org.chromium.mojo.system.MojoException;
 import org.chromium.mojom.device.BatteryMonitor;
 import org.chromium.mojom.device.BatteryStatus;
-import org.chromium.mojom.device.BatteryStatusObserver;
+
+import java.util.ArrayList;
+import java.util.List;
 
 /**
  * Android implementation of the battery monitor service defined in
@@ -16,12 +18,15 @@ import org.chromium.mojom.device.BatteryStatusObserver;
 public class BatteryMonitorImpl implements BatteryMonitor {
     // Factory that created this instance and notifies it about battery status changes.
     private final BatteryMonitorFactory mFactory;
+    private final List<QueryNextStatusResponse> mCallbacks;
+    private BatteryStatus mStatus;
+    private boolean mHasStatusToReport;
     private boolean mSubscribed;
 
-    private BatteryStatusObserver mClient;
-
     public BatteryMonitorImpl(BatteryMonitorFactory batteryMonitorFactory) {
         mFactory = batteryMonitorFactory;
+        mCallbacks = new ArrayList<QueryNextStatusResponse>();
+        mHasStatusToReport = false;
         mSubscribed = true;
     }
 
@@ -33,11 +38,6 @@ public class BatteryMonitorImpl implements BatteryMonitor {
     }
 
     @Override
-    public void setClient(BatteryStatusObserver client) {
-        mClient = client;
-    }
-
-    @Override
     public void close() {
         unsubscribe();
     }
@@ -47,12 +47,29 @@ public class BatteryMonitorImpl implements BatteryMonitor {
         unsubscribe();
     }
 
-    /**
-     * Notifies the client passing the given battery status information.
-     */
+    @Override
+    public void queryNextStatus(QueryNextStatusResponse callback) {
+        mCallbacks.add(callback);
+
+        if (mHasStatusToReport) {
+            reportStatus();
+        }
+    }
+
     void didChange(BatteryStatus batteryStatus) {
-        if (mClient != null) {
-            mClient.didChange(batteryStatus);
+        mStatus = batteryStatus;
+        mHasStatusToReport = true;
+
+        if (!mCallbacks.isEmpty()) {
+            reportStatus();
         }
-    };
+    }
+
+    void reportStatus() {
+        for (QueryNextStatusResponse callback : mCallbacks) {
+            callback.call(mStatus);
+        }
+        mCallbacks.clear();
+        mHasStatusToReport = false;
+    }
 }
diff --git a/device/battery/battery_monitor.mojom b/device/battery/battery_monitor.mojom
index 880685e..88a43d2 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]
 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.
+  QueryNextStatus() => (BatteryStatus status);
 };
diff --git a/device/battery/battery_monitor_impl.cc b/device/battery/battery_monitor_impl.cc
index dc07b62..62cbf60 100644
--- a/device/battery/battery_monitor_impl.cc
+++ b/device/battery/battery_monitor_impl.cc
@@ -17,20 +17,41 @@ void BatteryMonitorImpl::Create(
 BatteryMonitorImpl::BatteryMonitorImpl(
     mojo::InterfaceRequest<BatteryMonitor> request)
     : binding_(this, request.Pass()),
-      subscription_(BatteryStatusService::GetInstance()->AddCallback(
-          base::Bind(&BatteryMonitorImpl::DidChange, base::Unretained(this)))) {
+      status_to_report_(false) {
+  // NOTE: DidChange may be called before AddCallback returns. This is done to
+  // report current status.
+  subscription_ = BatteryStatusService::GetInstance()->AddCallback(
+      base::Bind(&BatteryMonitorImpl::DidChange, base::Unretained(this)));
 }
 
 BatteryMonitorImpl::~BatteryMonitorImpl() {
 }
 
+void BatteryMonitorImpl::QueryNextStatus(
+    const BatteryStatusCallback& callback) {
+  callbacks_.push_back(callback);
+
+  if (status_to_report_)
+    ReportStatus();
+}
+
 void BatteryMonitorImpl::RegisterSubscription() {
 }
 
 void BatteryMonitorImpl::DidChange(const BatteryStatus& battery_status) {
-  BatteryStatusPtr status(BatteryStatus::New());
-  *status = battery_status;
-  binding_.client()->DidChange(status.Pass());
+  status_ = battery_status;
+  status_to_report_ = true;
+
+  if (!callbacks_.empty())
+    ReportStatus();
+}
+
+void BatteryMonitorImpl::ReportStatus() {
+  for (const auto& callback : callbacks_)
+    callback.Run(status_.Clone());
+  callbacks_.clear();
+
+  status_to_report_ = false;
 }
 
 }  // namespace device
diff --git a/device/battery/battery_monitor_impl.h b/device/battery/battery_monitor_impl.h
index 7916b0d..49e85708 100644
--- a/device/battery/battery_monitor_impl.h
+++ b/device/battery/battery_monitor_impl.h
@@ -5,6 +5,8 @@
 #ifndef DEVICE_BATTERY_BATTERY_MONITOR_IMPL_H_
 #define DEVICE_BATTERY_BATTERY_MONITOR_IMPL_H_
 
+#include <vector>
+
 #include "base/memory/scoped_ptr.h"
 #include "device/battery/battery_export.h"
 #include "device/battery/battery_monitor.mojom.h"
@@ -19,14 +21,23 @@ class BatteryMonitorImpl : public BatteryMonitor {
       mojo::InterfaceRequest<BatteryMonitor> request);
 
  private:
+  typedef mojo::Callback<void(BatteryStatusPtr)> BatteryStatusCallback;
+
   explicit BatteryMonitorImpl(mojo::InterfaceRequest<BatteryMonitor> request);
   ~BatteryMonitorImpl() override;
 
+  // BatteryMonitor methods:
+  void QueryNextStatus(const BatteryStatusCallback& callback) override;
+
   void RegisterSubscription();
   void DidChange(const BatteryStatus& battery_status);
+  void ReportStatus();
 
   mojo::StrongBinding<BatteryMonitor> binding_;
   scoped_ptr<BatteryStatusService::BatteryUpdateSubscription> subscription_;
+  std::vector<BatteryStatusCallback> callbacks_;
+  BatteryStatus status_;
+  bool status_to_report_;
 
   DISALLOW_COPY_AND_ASSIGN(BatteryMonitorImpl);
 };
diff --git a/device/battery/battery_status_service.h b/device/battery/battery_status_service.h
index fd52b6b..a4cfac7d 100644
--- a/device/battery/battery_status_service.h
+++ b/device/battery/battery_status_service.h
@@ -30,6 +30,7 @@ class DEVICE_BATTERY_EXPORT BatteryStatusService {
 
   // Adds a callback to receive battery status updates.  Must be called on the
   // main thread. The callback itself will be called on the main thread as well.
+  // NOTE: The callback may be run before AddCallback returns!
   scoped_ptr<BatteryUpdateSubscription> AddCallback(
       const BatteryUpdateCallback& callback);