Make sure manifest specified shortcut for Extension Command can not override the built-in shortcuts.

chrome/browser/ui/gtk/extensions/extension_keybinding_registry_gtk.cc

Index: chrome/browser/ui/gtk/extensions/extension_keybinding_registry_gtk.cc
diff --git a/chrome/browser/ui/gtk/extensions/extension_keybinding_registry_gtk.cc b/chrome/browser/ui/gtk/extensions/extension_keybinding_registry_gtk.cc
index ccb02561afeac1e141559ed15d34d2f2ba7b729d..0a20b75a2e2afce4d6e7975cb485752f6dc0bc9f 100644
--- a/chrome/browser/ui/gtk/extensions/extension_keybinding_registry_gtk.cc
+++ b/chrome/browser/ui/gtk/extensions/extension_keybinding_registry_gtk.cc
@@ -9,6 +9,7 @@
 #include "chrome/browser/extensions/api/commands/command_service.h"
 #include "chrome/browser/extensions/extension_service.h"
 #include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/ui/gtk/accelerators_gtk.h"
 #include "chrome/common/extensions/extension.h"
 #include "ui/base/accelerators/platform_accelerator_gtk.h"
 
@@ -18,6 +19,19 @@ void extensions::ExtensionKeybindingRegistry::SetShortcutHandlingSuspended(
   ExtensionKeybindingRegistryGtk::set_shortcut_handling_suspended(suspended);
 }
 
+// static
+bool extensions::ExtensionKeybindingRegistry::IsChromeAccelerator(
+    const ui::Accelerator& accelerator) {
+  AcceleratorsGtk* accelerators = AcceleratorsGtk::GetInstance();
+  for (AcceleratorsGtk::const_iterator iter = accelerators->begin();
+       iter != accelerators->end(); ++iter) {
+    if (iter->second.key_code() == accelerator.key_code() &&
+        iter->second.modifiers() == accelerator.modifiers())
+      return true;
+  }
+  return false;
+}
+
 bool ExtensionKeybindingRegistryGtk::shortcut_handling_suspended_ = false;
 
 ExtensionKeybindingRegistryGtk::ExtensionKeybindingRegistryGtk(