Update to Chromium revision 6e53600d (#386251)

- Remove |accept_lang| parameter from CefJSDialogHandler::OnJSDialog
  and CefFormatUrlForSecurityDisplay (see https://crbug.com/336973#c36).
- Remove remaining NPAPI-related code including functions from
  cef_web_plugin.h (see https://crbug.com/493212#c55).
- Mac: 10.7+ deployment target is now required for client applications.
- Mac: Remove CefBrowserHost::SetWindowVisibility (issue #1375). No
  replacement is required for windowed rendering. Use WasHidden for
  off-screen rendering.
- Windows: Visual Studio 2015 Update 2 is now required when building
  CEF/Chromium.

patch/patches/gyp_331.patch

@@ -1,8 +1,8 @@
 diff --git gyp/generator/ninja.py gyp/generator/ninja.py
-index ffb3a85..02e0947 100644
+index edac48d..3bcc3b9 100644
 --- gyp/generator/ninja.py
 +++ gyp/generator/ninja.py
-@@ -747,7 +747,16 @@ class NinjaWriter(object):
+@@ -760,7 +760,16 @@ class NinjaWriter(object):
        for path in copy['files']:
          # Normalize the path so trailing slashes don't confuse us.
          path = os.path.normpath(path)