Issue #2019 - Do not dispatch keypress event for non-printable keys.

This will prevent the keypress DOM event from firing on keypresses
that do not produce printable keys (e.g. editing nav keys) in content.
This should not affect any chrome events that are in use.
Event dispatch can be re-enabled if necessary with the added pref.

widget/TextEventDispatcher.cpp

@@ -21,6 +21,7 @@ namespace widget {
  *****************************************************************************/
 
 bool TextEventDispatcher::sDispatchKeyEventsDuringComposition = false;
+bool TextEventDispatcher::sDispatchKeyPressEventNonPrintableInContent = false;
 
 TextEventDispatcher::TextEventDispatcher(nsIWidget* aWidget)
   : mWidget(aWidget)
@@ -36,6 +37,10 @@ TextEventDispatcher::TextEventDispatcher(nsIWidget* aWidget)
       &sDispatchKeyEventsDuringComposition,
       "dom.keyboardevent.dispatch_during_composition",
       false);
+    Preferences::AddBoolVarCache(
+      &sDispatchKeyPressEventNonPrintableInContent,
+      "dom.keyboardevent.keypress.dispatch_non_printable_in_content",
+      false);
     sInitialized = true;
   }
 }
@@ -531,6 +536,13 @@ TextEventDispatcher::DispatchKeyboardEventInternal(
     }
   }
 
+  if (!sDispatchKeyPressEventNonPrintableInContent &&
+      keyEvent.mMessage == eKeyPress &&
+      !keyEvent.IsInputtingText() &&
+      !keyEvent.IsInputtingLineBreak()) {
+    keyEvent.mFlags.mOnlySystemGroupDispatchInContent = true;
+  }
+
   DispatchInputEvent(mWidget, keyEvent, aStatus);
   return true;
 }

widget/TextEventDispatcher.h

@@ -399,6 +399,10 @@ private:
   // is a composition.
   static bool sDispatchKeyEventsDuringComposition;
 
+  // If this is true, keypress events for non-printable keys are dispatched to
+  // event listeners of the system event group in web content.
+  static bool sDispatchKeyPressEventNonPrintableInContent;
+
   nsresult BeginInputTransactionInternal(
              TextEventDispatcherListener* aListener,
              InputTransactionType aType);

widget/TextEvents.h

@@ -183,6 +183,30 @@ public:
     return IsKeyEventOnPlugin(mMessage);
   }
 
+  bool IsInputtingText() const
+  {
+    // NOTE: On some keyboard layouts, some characters are put in with Control
+    //       or Alt keys, but at that time, widget unsets the modifier flag
+    //       from the eKeyPress event, so it does not count as a modifier in
+    //       this check.
+    return mMessage == eKeyPress &&
+           mCharCode &&
+           !(mModifiers & (MODIFIER_ALT |
+                           MODIFIER_CONTROL |
+                           MODIFIER_META |
+                           MODIFIER_OS));
+  }
+
+  bool IsInputtingLineBreak() const
+  {
+    return mMessage == eKeyPress &&
+           mKeyNameIndex == KEY_NAME_INDEX_Enter &&
+           !(mModifiers & (MODIFIER_ALT |
+                           MODIFIER_CONTROL |
+                           MODIFIER_META |
+                           MODIFIER_OS));
+  }
+
   virtual WidgetEvent* Duplicate() const override
   {
     MOZ_ASSERT(mClass == eKeyboardEventClass,