views: Add support for absolute positioned overlay views.

To test:
Run `cefclient.exe --use-views --hide-frame --hide-controls`
Add `--enable-chrome-runtime` for the same behavior using the Chrome location
bar instead of a text field.

include/internal/cef_types.h

@@ -3198,6 +3198,17 @@ typedef enum {
   CEF_CTT_LOCATION,
 } cef_chrome_toolbar_type_t;
 
+///
+// Docking modes supported by CefWindow::AddOverlay.
+///
+typedef enum {
+  CEF_DOCKING_MODE_TOP_LEFT = 1,
+  CEF_DOCKING_MODE_TOP_RIGHT,
+  CEF_DOCKING_MODE_BOTTOM_LEFT,
+  CEF_DOCKING_MODE_BOTTOM_RIGHT,
+  CEF_DOCKING_MODE_CUSTOM,
+} cef_docking_mode_t;
+
 #ifdef __cplusplus
 }
 #endif