Switch from SI to IEC unit when formatting data usage bytes

- Created a new helper method DataUsageUtils.formatDataUsage() to
  format data usage bytes using IEC formatting.
- Switch from Formatter.formatFileSize() to DataUsageUtils.formatDataUsage()
  everywhere in datausage package.

Change-Id: I9323beed8bf5126b153fc9a3cdd9591c97ca6fd2
Merged-In: I9323beed8bf5126b153fc9a3cdd9591c97ca6fd2
Fixes: 76159924
Test: robotests

tests/robotests/src/com/android/settings/datausage/DataUsageUtilsTest.java

@@ -23,6 +23,7 @@ import static org.mockito.Mockito.when;
 import android.content.Context;
 import android.net.ConnectivityManager;
 import android.telephony.TelephonyManager;
+import android.util.DataUnit;
 
 import com.android.settings.testutils.SettingsRobolectricTestRunner;
 
@@ -78,4 +79,12 @@ public final class DataUsageUtilsTest {
         boolean hasSim = DataUsageUtils.hasSim(mContext);
         assertThat(hasSim).isFalse();
     }
+
+    @Test
+    public void formatDataUsage_useIECUnit() {
+        final CharSequence formattedDataUsage = DataUsageUtils.formatDataUsage(
+                mContext, DataUnit.GIBIBYTES.toBytes(1));
+
+        assertThat(formattedDataUsage).isEqualTo("1.00 GB");
+    }
 }