Change browser/page action default icon defined in manifest to support hidpi.

chrome/common/extensions/extension_manifest_constants.cc

Index: chrome/common/extensions/extension_manifest_constants.cc
diff --git a/chrome/common/extensions/extension_manifest_constants.cc b/chrome/common/extensions/extension_manifest_constants.cc
index ad5e4463af89a82b7a6fb50802c4e549f287ef97..8af7c2a52999cbb0f39510a7c9e41b9358363ce1 100644
--- a/chrome/common/extensions/extension_manifest_constants.cc
+++ b/chrome/common/extensions/extension_manifest_constants.cc
@@ -77,6 +77,7 @@ const char kOptionalPermissions[] = "optional_permissions";
 const char kOptionsPage[] = "options_page";
 const char kPageAction[] = "page_action";
 const char kPageActionDefaultIcon[] = "default_icon";
+const char kPageActionDefaultIconSet[] = "default_icon_set";
 const char kPageActionDefaultPopup[] = "default_popup";
 const char kPageActionDefaultTitle[] = "default_title";
 const char kPageActionIcons[] = "icons";