Adding StorageStats API to get external cache size

Test: atest StorageHostTest and also manually using StorageTestApp
to use the API and display the cache size.

Bug: 175016452
Change-Id: Iff0503c1643ee5fc501037e413aa4b5461ca3388

core/api/current.txt

@@ -8163,6 +8163,7 @@ package android.app.usage {
     method public long getAppBytes();
     method public long getCacheBytes();
     method public long getDataBytes();
+    method public long getExternalCacheBytes();
     method public void writeToParcel(android.os.Parcel, int);
     field @NonNull public static final android.os.Parcelable.Creator<android.app.usage.StorageStats> CREATOR;
   }

core/java/android/app/usage/StorageStats.java

@@ -32,6 +32,7 @@ public final class StorageStats implements Parcelable {
     /** {@hide} */ public long codeBytes;
     /** {@hide} */ public long dataBytes;
     /** {@hide} */ public long cacheBytes;
+    /** {@hide} */ public long externalCacheBytes;
 
     /**
      * Return the size of app. This includes {@code APK} files, optimized
@@ -77,6 +78,17 @@ public final class StorageStats implements Parcelable {
         return cacheBytes;
     }
 
+    /**
+     * Return the size of all cached data in the primary external/shared storage.
+     * This includes files stored under
+     * {@link Context#getExternalCacheDir()}.
+     * <p>
+     * Cached data is isolated for each user on a multiuser device.
+     */
+    public @BytesLong long getExternalCacheBytes() {
+        return externalCacheBytes;
+    }
+
     /** {@hide} */
     public StorageStats() {
     }
@@ -86,6 +98,7 @@ public final class StorageStats implements Parcelable {
         this.codeBytes = in.readLong();
         this.dataBytes = in.readLong();
         this.cacheBytes = in.readLong();
+        this.externalCacheBytes = in.readLong();
     }
 
     @Override
@@ -98,6 +111,7 @@ public final class StorageStats implements Parcelable {
         dest.writeLong(codeBytes);
         dest.writeLong(dataBytes);
         dest.writeLong(cacheBytes);
+        dest.writeLong(externalCacheBytes);
     }
 
     public static final @android.annotation.NonNull Creator<StorageStats> CREATOR = new Creator<StorageStats>() {

services/usage/java/com/android/server/usage/StorageStatsService.java

@@ -514,6 +514,7 @@ public class StorageStatsService extends IStorageStatsManager.Stub {
         res.codeBytes = stats.codeSize + stats.externalCodeSize;
         res.dataBytes = stats.dataSize + stats.externalDataSize;
         res.cacheBytes = stats.cacheSize + stats.externalCacheSize;
+        res.externalCacheBytes = stats.externalCacheSize;
         return res;
     }