Move //device/generic_sensor to be part of the internal implementation of the Device Service.

services/device/public/interfaces/BUILD.gn

Index: services/device/public/interfaces/BUILD.gn
diff --git a/services/device/public/interfaces/BUILD.gn b/services/device/public/interfaces/BUILD.gn
index ea9dd259754799d5d553bdbef50b522ff7ff381d..e4f3123e4cff4eef64446f03a8ca78b7bd06bd86 100644
--- a/services/device/public/interfaces/BUILD.gn
+++ b/services/device/public/interfaces/BUILD.gn
@@ -22,6 +22,20 @@ mojom("interfaces") {
   use_once_callback = false
 }
 
+mojom("generic_sensor") {

[ke.he, 2017/05/17 09:32:05]

The reason I didn't merge "generic_sensor" target into "interfaces" because
there is cycle dependency between its mojom files and cpp library files.

generic_sensor's mojom depends on their traits file "sensor_struct_traits.cc";
The "sensor_struct_traits.cc" includes its cpp library file
"platform_sensor_configuration.h";
The "platform_sensor_configuraton.cpp" includes "sensor.mojom.h". It is a cycle.
So If the target that depends on generic_sensor:interface must also depends on
generic_sensor's cpp library if it wants to do link.

In //service/device/fingerprints/BUILD.gn, there is target
component("fingerprint") deps on //service/device/public/interfaces, it doesn't
depend on generic_sensor's cpp library. 

[ke.he, 2017/05/18 05:24:18]

Correction:
The GN target that depends on ".../cpp/generic_sensor:interface" must also
depend on
generic_sensor's cpp library if it wants to link to generate a *.so.

[Reilly Grant (use Gerrit), 2017/05/18 15:58:49]

I resolved a similar cycle in //device/usb/BUILD.gn by depending on header
generation instead of binary compilation:

https://cs.chromium.org/chromium/src/device/usb/BUILD.gn?q=usb/BUILD.gn&l=70

+  sources = [
+    "sensor.mojom",
+    "sensor_provider.mojom",
+  ]
+
+  public_deps = [
+    ":constants",
+  ]
+
+  # TODO(crbug.com/714018): Convert the implementation to use OnceCallback.
+  use_once_callback = false
+}
+
 mojom("constants") {
   sources = [
     "constants.mojom",