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;
 }