Clean up HID backend and API.

device/hid/hid_utils_mac.cc

Index: device/hid/hid_utils_mac.cc
diff --git a/device/hid/hid_utils_mac.cc b/device/hid/hid_utils_mac.cc
index 588041a3ccb2b3c614b29c413236302d2af731fb..3750db95d47f0af67594d7539a3f55d978f77420 100644
--- a/device/hid/hid_utils_mac.cc
+++ b/device/hid/hid_utils_mac.cc
@@ -16,17 +16,30 @@
 
 namespace device {
 
-bool GetHidIntProperty(IOHIDDeviceRef device,
-                       CFStringRef key,
-                       int32_t* result) {
+int32_t GetHidIntProperty(IOHIDDeviceRef device, CFStringRef key) {
+  int32_t value;
+  if (TryGetHidIntProperty(device, key, &value))
+    return value;
+  return 0;
+}
+
+std::string GetHidStringProperty(IOHIDDeviceRef device, CFStringRef key) {
+  std::string value;
+  TryGetHidStringProperty(device, key, &value);
+  return value;
+}
+
+bool TryGetHidIntProperty(IOHIDDeviceRef device,
+                          CFStringRef key,
+                          int32_t* result) {
   CFNumberRef ref = base::mac::CFCast<CFNumberRef>(

[Mark Mentovai, 2014/02/13 22:37:51]

You might think this is crazy-paranoid (and we can talk about it if you do), but
you might want to add something that makes sure that the number actually fits
into an int32_t. There’s CFNumberGetType, but it’s clunky to use. Unfortunately,
there’s no really good way to ask a CFNumber (or an NSNumber) “hey, will your
value fit into this data type without truncation or sign-flipping?”

[Ken Rockot(use gerrit already), 2014/02/18 19:43:09]

I would be happy to add this, but it does look like it would be cumbersome. I'm
imagining that the result of CFNumberGetType would have to be tested against the
set kCFNumber{SInt8, SInt16, SIn32, Float32, Char, [additional compiler
dependent types]}Type.

       IOHIDDeviceGetProperty(device, key));
   return ref && CFNumberGetValue(ref, kCFNumberSInt32Type, result);
 }
 
-bool GetHidStringProperty(IOHIDDeviceRef device,
-                          CFStringRef key,
-                          std::string* result) {
+bool TryGetHidStringProperty(IOHIDDeviceRef device,
+                             CFStringRef key,
+                             std::string* result) {
   CFStringRef ref = base::mac::CFCast<CFStringRef>(
       IOHIDDeviceGetProperty(device, key));
   if (!ref) {