Auto merge of #6495 - jruderman:add_keyboard_shortcuts_2, r=metajack

Add keyboard shortcuts to glutin browser

Supersedes #6488. Changes since then:

* Fix a few places where we needed cfg(feature = "window") in order to compile without the feature.
* Zoom-in shortcut now works both with and without shift. (Uses a guard because I couldn't think of another way to do it without CTFE.)
* Back/forward shortcuts now correctly use Alt on non-Mac platforms.
* The back/forward shortcuts that use square brackets are now non-Windows, rather than Mac-only. This roughly matches XP_UNIX: http://hg.mozilla.org/mozilla-central/file/d4c4ce7f060c/browser/base/content/browser-sets.inc#l354

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components/compositing/compositor.rs

@@ -851,6 +851,10 @@ impl<Window: WindowMethods> IOCompositor<Window> {
                 self.on_zoom_window_event(magnification);
             }
 
+            WindowEvent::ResetZoom => {
+                self.on_zoom_reset_window_event();
+            }
+
             WindowEvent::PinchZoom(magnification) => {
                 self.on_pinch_zoom_window_event(magnification);
             }
@@ -1066,6 +1070,12 @@ impl<Window: WindowMethods> IOCompositor<Window> {
         self.scene.set_root_layer_size(self.window_size.as_f32());
     }
 
+    fn on_zoom_reset_window_event(&mut self) {
+        self.page_zoom = ScaleFactor::new(1.0);
+        self.update_zoom_transform();
+        self.send_window_size();
+    }
+
     fn on_zoom_window_event(&mut self, magnification: f32) {
         self.page_zoom = ScaleFactor::new((self.page_zoom.get() * magnification).max(1.0));
         self.update_zoom_transform();

components/compositing/windowing.rs

@@ -64,6 +64,8 @@ pub enum WindowEvent {
     Zoom(f32),
     /// Simulated "pinch zoom" gesture for non-touch platforms (e.g. ctrl-scrollwheel).
     PinchZoom(f32),
+    /// Sent when the user resets zoom to default.
+    ResetZoom,
     /// Sent when the user uses chrome navigation (i.e. backspace or shift-backspace).
     Navigation(WindowNavigateMsg),
     /// Sent when the user quits the application
@@ -86,6 +88,7 @@ impl Debug for WindowEvent {
             WindowEvent::Scroll(..) => write!(f, "Scroll"),
             WindowEvent::Zoom(..) => write!(f, "Zoom"),
             WindowEvent::PinchZoom(..) => write!(f, "PinchZoom"),
+            WindowEvent::ResetZoom => write!(f, "ResetZoom"),
             WindowEvent::Navigation(..) => write!(f, "Navigation"),
             WindowEvent::Quit => write!(f, "Quit"),
         }

components/msg/constellation_msg.rs

@@ -192,6 +192,7 @@ pub enum Key {
 
 bitflags! {
     flags KeyModifiers: u8 {
+        const NONE = 0x00,
         const SHIFT = 0x01,
         const CONTROL = 0x02,
         const ALT = 0x04,