Map signal_strength from percentage to dBm per spec

chrome/browser/chromeos/policy/device_status_collector.cc

Index: chrome/browser/chromeos/policy/device_status_collector.cc
diff --git a/chrome/browser/chromeos/policy/device_status_collector.cc b/chrome/browser/chromeos/policy/device_status_collector.cc
index d57319303d5a9686fe006802023ddd130fa5da19..9c43fc886570bf02f73ebe32a274243849dae953 100644
--- a/chrome/browser/chromeos/policy/device_status_collector.cc
+++ b/chrome/browser/chromeos/policy/device_status_collector.cc
@@ -636,6 +636,22 @@ void DeviceStatusCollector::GetLocation(
   }
 }
 
+int DeviceStatusCollector::ConvertSignalStrength(int signal_strength) {
+  // Shill attempts to convert attempts to convert from its internal dBm to a

[Thiemo Nagel, 2015/04/16 15:16:33]

Please remove duplicate "attempts to convert".

[Andrew T Wilson (Slow), 2015/04/17 14:41:02]

Done.

+  // percentage range (from 1-100) by subtracting 120 from the raw dBm value,

[Thiemo Nagel, 2015/04/16 15:16:33]

s/1-100/0-100/
s/substracting 120 from/adding 120 to/

[Andrew T Wilson (Slow), 2015/04/17 14:41:02]

Done.

+  // and then clamping the result to the range 1-100.

[Thiemo Nagel, 2015/04/16 15:16:33]

s/1-100/0-100/

I'd suggest to include some kind of cross-reference to the shill function, eg.
its name "shill::WiFiService::SignalToStrength()".

[Andrew T Wilson (Slow), 2015/04/17 14:41:02]

Done.

+  //
+  // To convert back to dBm, we subtract 120 from the percentage value to yield
+  // a clamped dBm value in the range of -119 to -20dBm.
+  //
+  // TODO(atwilson): Tunnel the raw dBm signal strength from Shill instead of
+  // doing the conversion here so we can report non-clamped values
+  // (crbug.com/463334).
+  DCHECK_GT(signal_strength, 0);
+  DCHECK_LE(signal_strength, 100);
+  return signal_strength - 120;
+}
+
 void DeviceStatusCollector::GetNetworkInterfaces(
     em::DeviceStatusReportRequest* request) {
   // Maps shill device type strings to proto enum constants.
@@ -728,7 +744,12 @@ void DeviceStatusCollector::GetNetworkInterfaces(
     // Copy fields from NetworkState into the status report.
     em::NetworkState* proto_state = request->add_network_state();
     proto_state->set_connection_state(connection_state_enum);
-    proto_state->set_signal_strength(state->signal_strength());
+    // If shill has provided a signal strength, convert it to dBm and store it

[Thiemo Nagel, 2015/04/16 15:16:33]

As far as I can see, this specific conversion should be limited to wifi
networks.  Also, it seems that zero signal strength implies "no measurement"
only for wifi (and wimax).

[Andrew T Wilson (Slow), 2015/04/17 14:41:02]

Only report this now for wifi networks.

+    // in the status report.
+    if (state->signal_strength()) {
+      proto_state->set_signal_strength(
+          ConvertSignalStrength(state->signal_strength()));
+    }
     if (!state->device_path().empty())
       proto_state->set_device_path(state->device_path());