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

public/platform/WebGamepad.h

Index: public/platform/WebGamepad.h
diff --git a/public/platform/WebGamepad.h b/public/platform/WebGamepad.h
index b2f32da02f57a3a4ef1a03469f14e541e29605d3..6d079a035bfbbc6616b925415106c0cdcf4c30b3 100644
--- a/public/platform/WebGamepad.h
+++ b/public/platform/WebGamepad.h
@@ -30,6 +30,9 @@
 #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)
@@ -38,16 +41,16 @@ 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
@@ -84,7 +87,7 @@ public:
     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;
@@ -97,7 +100,7 @@ public:
 };
 
 #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)