Add UsageDetails dictionary.

    squash 47187f6 Address style nits from domenic.
    squash 0fd3b44 Explicitly define each storage system's usage.

storage.bs

@@ -18,7 +18,7 @@ these APIs by defining:
 <ul class=brief>
  <li>A bucket, the primitive these APIs store their data in
  <li>A way of making that bucket persistent
- <li>A way of getting usage and quota estimates for an <a for=/>origin</a>
+ <li>A way of getting usage, quota, and per-system usage estimates for an <a for=/>origin</a>
 </ul>
 
 <p>Traditionally, as the user runs out of storage space on their device, the data stored with these
@@ -178,7 +178,18 @@ larger <a>site storage quota</a>. Factors such as navigation frequency, recency
 bookmarking, and <a href="#persistence">permission</a> for {{"persistent-storage"}} can be used as
 indications of "popularity".
 
+The <dfn export>application cache site storage usage</dfn> for an origin is a rough estimate of the amount
+of bytes used in Application Cache in <var>origin</var>'s <a>site storage unit</a>. [[HTML#appcache]]
 
+The <dfn export>caches site storage usage</dfn> for an origin is a rough estimate of the amount
+of bytes used in Cache API in <var>origin</var>'s <a>site storage unit</a>. [[service-workers-1#cache-objects]]
+
+The <dfn export>indexedDB site storage usage</dfn> for an origin is a rough estimate of the amount
+of bytes used in IndexedDB in <var>origin</var>'s <a>site storage unit</a>. [[IndexedDB]]
+
+The <dfn export>service worker registration site storage usage</dfn> for an origin is a rough
+estimate of the amount of bytes used in service worker registrations in <var>origin</var>'s
+<a>site storage unit</a>. [[service-workers-1]]
 
 <h2 id=ui-guidelines>User Interface Guidelines</h2>
 
@@ -234,7 +245,16 @@ interface StorageManager {
 dictionary StorageEstimate {
   unsigned long long usage;
   unsigned long long quota;
+  StorageUsageDetails usageDetails;
 };
+
+dictionary StorageUsageDetails {
+  unsigned long long applicationCache;
+  unsigned long long caches;
+  unsigned long long indexedDB;
+  unsigned long long serviceWorkerRegistrations;
+};
+
 </pre>
 
 The <dfn method for=StorageManager><code>persisted()</code></dfn> method, when invoked, must run
@@ -331,8 +351,26 @@ must run these steps:
 
    <li><p>Let <var>quota</var> be <a>site storage quota</a> for <var>origin</var>.
 
-   <li><p>Let <var>dictionary</var> be a new {{StorageEstimate}} dictionary whose {{usage}} member
-   is <var>usage</var> and {{quota}} member is <var>quota</var>.
+   <li><p>Let <var>applicationCache</var> be <a>application cache site storage usage</a>
+   for <var>origin</var>.
+
+   <li><p>Let <var>indexedDB</var> be <a>indexedDB site storage usage</a> for <var>origin</var>.
+
+   <li><p>Let <var>caches</var> be <a>caches site storage usage</a> for <var>origin</var>.
+
+   <li><p>Let <var>serviceWorkerRegistrations</var> be <a>service worker registration
+   site storage usage</a> for <var>origin</var>.
+
+   <li><p>Let <var>usageDetails</var> be a new {{StorageUsageDetails}} dictionary
+   whose {{StorageUsageDetails/applicationCache}} member is <var>applicationCache</var>,
+   {{StorageUsageDetails/indexedDB}} member is <var>indexedDB</var>, {{StorageUsageDetails/caches}}
+   member is <var>caches</var>, and {{StorageUsageDetails/serviceWorkerRegistrations}} member is
+   <var>serviceWorkerRegistrations</var>. Any member for which the <a>site storage usage</a>
+   is less than 0 should be excluded from the {{StorageUsageDetails}} dictionary.
+
+   <li><p>Let <var>dictionary</var> be a new {{StorageEstimate}} dictionary whose {{StorageEstimate/usage}} member
+   is <var>usage</var>, {{StorageEstimate/quota}} member is <var>quota</var> and {{usageDetails}}
+   member is <var>usageDetails</var>.
 
    <li>
     <p>If there was an internal error while obtaining <var>usage</var> and <var>quota</var>, then