Apply fixes for EfficientStrings.

Refactoring to avoid StringBuffer synchronization overhead.

Bug: 170978902
Test: none
Exempt-From-Owner-Approval: trivial refactoring
Change-Id: Ibf843ed780c1202d5d96a11eaca889e592f19263

core/java/android/util/proto/EncodedBuffer.java

@@ -648,7 +648,7 @@ public final class EncodedBuffer {
      * Print the internal buffer chunks.
      */
     private static int dumpByteString(String tag, String prefix, int start, byte[] buf) {
-        StringBuffer sb = new StringBuffer();
+        StringBuilder sb = new StringBuilder();
         final int length = buf.length;
         final int lineLen = 16;
         int i;
@@ -656,7 +656,7 @@ public final class EncodedBuffer {
             if (i % lineLen == 0) {
                 if (i != 0) {
                     Log.d(tag, sb.toString());
-                    sb = new StringBuffer();
+                    sb = new StringBuilder();
                 }
                 sb.append(prefix);
                 sb.append('[');