MacViews: Handle Space and Return keys correctly for Buttons.

ui/views/style/platform_style_mac.mm

Index: ui/views/style/platform_style_mac.mm
diff --git a/ui/views/style/platform_style_mac.mm b/ui/views/style/platform_style_mac.mm
index 4e07484e09028f50267ef9ee6733c3df515457f9..d747cefa394447c74f24a1eb66395d4de7a7a615 100644
--- a/ui/views/style/platform_style_mac.mm
+++ b/ui/views/style/platform_style_mac.mm
@@ -37,6 +37,13 @@
 const CustomButton::NotifyAction PlatformStyle::kMenuNotifyActivationAction =
     CustomButton::NOTIFY_ON_PRESS;
 
+const CustomButton::ClickAction PlatformStyle::kClickActionOnSpace =
+    CustomButton::CLICK_ON_PRESS;
+
+// On Mac, the Return Key is used to perform the default action even when a
+// control is focused.

[tapted, 2017/01/05 00:34:41]

With extended comment in platform_style.h, this comment can probably be dropped.

[karandeepb, 2017/01/05 10:50:09]

I'll let this remain since this explains that Return is bound to the default
dialog action, which is something not captured in the comment in
platform_style.h.

+const bool PlatformStyle::kReturnClicksFocusedControl = false;
+
 // static
 gfx::ImageSkia PlatformStyle::CreateComboboxArrow(bool is_enabled,
                                                   Combobox::Style style) {