Add a UI for setting JS flags.

The UI only shows up when 'about:debug' is typed in the address bar.
JS flags are a string '--heap-stats --log-gc' in V8 etc.

Currently this is only used by V8 build for debugging purpose.
diff --git a/res/values/strings.xml b/res/values/strings.xml
index 68742e1..8d31462 100644
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -431,6 +431,8 @@
     <!-- Do not tranlsate.  Development option -->
     <string name="pref_development_search_url" translatable="false">Set search URL</string>
     <!-- Do not tranlsate.  Development option -->
+    <string name="js_engine_flags" translatable="false">Set JS flags</string>
+    <!-- Do not tranlsate.  Development option -->
     <string name="pref_development_uastring" translatable="false">UAString</string>
     <!-- Do not tranlsate.  Development option -->
     <string-array name="pref_development_ua_choices" translatable="false">
diff --git a/res/xml/debug_preferences.xml b/res/xml/debug_preferences.xml
index 4f55f6b..c39ae5b 100644
--- a/res/xml/debug_preferences.xml
+++ b/res/xml/debug_preferences.xml
@@ -51,9 +51,14 @@
             android:title="@string/pref_development_nav_dump" />
 
         <com.android.browser.BrowserSearchpagePreference
-                android:key="search_url" 
-                android:title="@string/pref_development_search_url"
-                android:singleLine="true" />
+            android:key="search_url"
+            android:title="@string/pref_development_search_url"
+            android:singleLine="true" />
+
+        <EditTextPreference
+            android:key="js_engine_flags"
+            android:title="@string/js_engine_flags"
+            android:singleLine="true" />
 
         <ListPreference
             android:key="user_agent"