Update Gamepad.axes / GamepadButton.value to match the latest specification

public/platform/WebGamepad.h

 // Copyright (C) 2011, Google Inc. All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are met:
 //
 // 1. Redistributions of source code must retain the above copyright
 //    notice, this list of conditions and the following disclaimer.
 // 2. Redistributions in binary form must reproduce the above copyright
 //    notice, this list of conditions and the following disclaimer in the
 //    documentation and/or other materials provided with the distribution.
@@ skipping 12 matching lines @@
 
 #ifndef WebGamepad_h
 #define WebGamepad_h
 
 #include "WebCommon.h"
 
 #if BLINK_IMPLEMENTATION
 #include "wtf/Assertions.h"
 #endif
 
+// FIXME(cdumez): Remove once the Chromium side has been updated.
+#define ENABLE_NEW_GAMEPAD_API 1

[dmichael (off chromium), 2014/05/21 16:49:31]

I don't think this is safe. You have Chromium code that conditionally compiles
based on this:
https://codereview.chromium.org/280713004/diff/100001/ppapi/shared_impl/ppb_g...
When compiling a translation unit, you might or might not get this #define,
depending on if this file is included at all, and when it is included. I.e., If
WebGamepad.h is included *Before* ppb_gamepad_shared.h, then WebKitGamepad in
ppb_gamepad_shared.h will use double in *that* translation unit. In that case,
it won't match the definition of WebKitGamepad that was compiled for the
ppb_gamepad_shared.cc, so you'll get a linker error, I think.

If WebGamepad.h is included *After* ppb_gamepad_shared.h, then WebKitGamepad in
ppb_gamepad_shared.h uses floats instead of doubles, so the sizes won't match.
This is probably why you get an error building pepper_plugin_instance_impl.cc
with this change.

I suspect the easiest way to fix this is to just define ENABLE_NEW_GAMEPAD_API=1
in GYP for all targets that are dependent on blink. That should flip the switch
all over the relevant parts of the Chromium build to make sure it starts
building the "double" version in all translation units.

If that doesn't work, you might need a more complicated DEPS dance where you
make WebGamepad depend on the same #define to conditionally compile the same
way. Then flip on ENABLE_NEW_GAMEPAD_API in chromium temporarily. *Then* you'd
be able to remove the conditional compilation stuff in blink and chromium.

+
 namespace blink {
 
 #pragma pack(push, 1)
 
 class WebGamepadButton {
 public:
     WebGamepadButton()
         : pressed(false)
-        , value(0.f)
+        , value(0.)
     {
     }
-    WebGamepadButton(bool pressed, float value)
+    WebGamepadButton(bool pressed, double value)
         : pressed(pressed)
         , value(value)
     {
     }
     bool pressed;
-    float value;
+    double value;
 };
 
 // This structure is intentionally POD and fixed size so that it can be shared
 // memory between hardware polling threads and the rest of the browser. See
 // also WebGamepads.h.
 class WebGamepad {
 public:
     static const size_t idLengthCap = 128;
     static const size_t mappingLengthCap = 16;
     static const size_t axesLengthCap = 16;
@@ skipping 16 matching lines @@
     WebUChar id[idLengthCap];
 
     // Monotonically increasing value referring to when the data were last
     // updated.
     unsigned long long timestamp;
 
     // Number of valid entries in the axes array.
     unsigned axesLength;
 
     // Normalized values representing axes, in the range [-1..1].
-    float axes[axesLengthCap];
+    double axes[axesLengthCap];
 
     // Number of valid entries in the buttons array.
     unsigned buttonsLength;
 
     // Button states
     WebGamepadButton buttons[buttonsLengthCap];
 
     // Mapping type (for example "standard")
     WebUChar mapping[mappingLengthCap];
 };
 
 #if BLINK_IMPLEMENTATION
-COMPILE_ASSERT(sizeof(WebGamepad) == 529, WebGamepad_has_wrong_size);
+COMPILE_ASSERT(sizeof(WebGamepad) == 721, WebGamepad_has_wrong_size);
 #endif
 
 #pragma pack(pop)
 
 }
 
 #endif // WebGamepad_h