[Device Service] Move Gamepad Blink headers to be part of the Gamepad client library

content/test/DEPS

 include_rules = [
   # Allow inclusion of specific components that we depend on.
   # See comment in content/DEPS for which components are allowed.
   "+components/leveldb",
   "+components/scheduler/renderer",
   "+components/scheduler/test",
 
   "+cc/blink",
   "+chromeos/audio", # For WebRTC tests.
   # Testing utilities can access anything in content/
   "+content",
   "+device/bluetooth", # For WebBluetooth tests
+  "+device/gamepad/public/cpp",
   "+device/sensors/public/cpp",
   # For loading V8's initial snapshot from external files.
   "+gin/v8_initializer.h",
   "+services/catalog",
   "+ui/base/resource/data_pack.h",
   "+ui/base/resource/resource_bundle.h",
   "!v8/include/v8.h",
 ]
 
 specific_include_rules = {
   "layouttest_support.cc": [
     "+content/shell/test_runner",
     "+content/shell/common/shell_switches.h",
     "+services/ui/public/cpp/gpu",
   ],
 }