Browser: add save path setting feature and full indicator

1. The saving path can be preseted,
   both the internal storage and the SD card are supported
2. Reminder if the download file size exceed the available
   memory.

CRs-fixed: 507953 507954

Change-Id: Ic2f807cb0ee2408cc6e4455a4c67bab5a0d01a8f
diff --git a/src/com/android/browser/PreferenceKeys.java b/src/com/android/browser/PreferenceKeys.java
index 1828032..ffbb39a 100644
--- a/src/com/android/browser/PreferenceKeys.java
+++ b/src/com/android/browser/PreferenceKeys.java
@@ -47,7 +47,8 @@
     static final String PREF_SEARCH_ENGINE = "search_engine";
     static final String PREF_WEBSITE_SETTINGS = "website_settings";
     static final String PREF_ALLOW_APP_TABS = "allow_apptabs";
-
+    // Keys for download path settings
+    static final String PREF_DOWNLOAD_PATH = "download_path_setting_screen";
     // ----------------------
     // Keys for debug_preferences.xml
     // ----------------------