Bug 1359471 - Add a checkbox to disable the cache smart size. r=jorgk

mail/components/preferences/advanced.js

@@ -186,6 +186,21 @@ var gAdvancedPane = {
     } catch (e) {}
   },
 
+  updateCacheSizeUI: function (smartSizeEnabled)
+  {
+    document.getElementById("useCacheBefore").disabled = smartSizeEnabled;
+    document.getElementById("cacheSize").disabled = smartSizeEnabled;
+    document.getElementById("useCacheAfter").disabled = smartSizeEnabled;
+  },
+
+  readSmartSizeEnabled: function ()
+  {
+    // The smart_size.enabled preference element is inverted="true", so its
+    // value is the opposite of the actual pref value
+    var disabled = document.getElementById("browser.cache.disk.smart_size.enabled").value;
+    this.updateCacheSizeUI(!disabled);
+  },
+
   /**
    * Converts the cache size from units of KB to units of MB and returns that
    * value.

mail/components/preferences/advanced.xul

@@ -91,6 +91,10 @@
                   name="mail.purge_threshhold_mb" type="int"/>
       <preference id="browser.cache.disk.capacity"
                   name="browser.cache.disk.capacity" type="int"/>
+      <preference id="browser.cache.disk.smart_size.enabled"
+                  name="browser.cache.disk.smart_size.enabled"
+                  inverted="true"
+                  type="bool"/>
 #ifdef MOZ_UPDATER
       <!-- Update tab -->
       <preference id="app.update.enabled" name="app.update.enabled"
@@ -310,7 +314,14 @@ type="bool"/>
                       label="&clearCacheNow.label;" accesskey="&clearCacheNow.accesskey;"
                       oncommand="gAdvancedPane.clearCache();"/>
             </hbox>
-            <hbox align="center">
+            <hbox>
+              <checkbox preference="browser.cache.disk.smart_size.enabled"
+                        id="allowSmartSize"
+                        onsyncfrompreference="return gAdvancedPane.readSmartSizeEnabled();"
+                        label="&overrideSmartCacheSize.label;"
+                        accesskey="&overrideSmartCacheSize.accesskey;"/>
+            </hbox>
+            <hbox align="center" class="indent">
               <label id="useCacheBefore" control="cacheSize"
                      accesskey="&useCacheBefore.accesskey;" value="&useCacheBefore.label;"/>
               <textbox id="cacheSize" type="number" size="4" max="1024"

mail/locales/en-US/chrome/messenger/preferences/advanced.dtd

@@ -89,6 +89,8 @@
 <!ENTITY useCacheBefore.label            "Use up to">
 <!ENTITY useCacheBefore.accesskey        "U">
 <!ENTITY useCacheAfter.label             "MB of space for the cache">
+<!ENTITY overrideSmartCacheSize.label    "Override automatic cache management">
+<!ENTITY overrideSmartCacheSize.accesskey "v">
 <!ENTITY clearCacheNow.label             "Clear Now">
 <!ENTITY clearCacheNow.accesskey         "C">