Updating Gamepad API to match latest spec

ppapi/shared_impl/ppb_gamepad_shared.h

Index: ppapi/shared_impl/ppb_gamepad_shared.h
diff --git a/ppapi/shared_impl/ppb_gamepad_shared.h b/ppapi/shared_impl/ppb_gamepad_shared.h
index 821980f3aa72ef676d92402cce581d5aa4507438..b3377f2e1d122ab1139daff24aebbdd7e8a7d469 100644
--- a/ppapi/shared_impl/ppb_gamepad_shared.h
+++ b/ppapi/shared_impl/ppb_gamepad_shared.h
@@ -17,10 +17,16 @@ namespace ppapi {
 
 #pragma pack(push, 1)
 
+struct WebKitGamepadButton {
+    bool pressed;
+    float value;
+};
+
 // This must match the definition of blink::Gamepad. The GamepadHost unit test
 // has some compile asserts to validate this.
 struct WebKitGamepad {
     static const size_t kIdLengthCap = 128;
+    static const size_t kMappingLengthCap = 16;
     static const size_t kAxesLengthCap = 16;
     static const size_t kButtonsLengthCap = 32;
 
@@ -44,7 +50,10 @@ struct WebKitGamepad {
     unsigned buttons_length;
 
     // Normalized values representing buttons, in the range [0..1].
-    float buttons[kButtonsLengthCap];
+    WebKitGamepadButton buttons[kButtonsLengthCap];
+
+    // Mapping type (for example "standard")
+    base::char16 mapping[kMappingLengthCap];
 };
 
 // This must match the definition of blink::Gamepads. The GamepadHost unit