Fix ParsableByteArray.readLine + discard BOM at start of line.

- I think \r and \n are handled the wrong way around?
- We only expect to encounter a BOM sequence at the start of a
  file, but it feels fine to automatically discard it in all
  cases for simplicity. A BOM sequence doesn't mean anything in
  UTF-8. See https://en.wikipedia.org/wiki/Byte_order_mark. Note
  that I think the advice not to remove it on that page relates
  only to the case where the file is being edited + saved.

Issue #1136
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112143407

library/src/androidTest/assets/subrip/typical_with_byte_order_mark

@@ -0,0 +1,12 @@
+1
+00:00:00,000 --> 00:00:01,234
+This is the first subtitle.
+
+2
+00:00:02,345 --> 00:00:03,456
+This is the second subtitle.
+Second subtitle with second line.
+
+3
+00:00:04,567 --> 00:00:08,901
+This is the third subtitle.

library/src/androidTest/java/com/google/android/exoplayer/text/subrip/SubripParserTest.java

@@ -28,6 +28,7 @@ public final class SubripParserTest extends InstrumentationTestCase {
 
   private static final String EMPTY_FILE = "subrip/empty";
   private static final String TYPICAL_FILE = "subrip/typical";
+  private static final String TYPICAL_WITH_BYTE_ORDER_MARK = "subrip/typical_with_byte_order_mark";
   private static final String TYPICAL_EXTRA_BLANK_LINE = "subrip/typical_extra_blank_line";
   private static final String TYPICAL_MISSING_TIMECODE = "subrip/typical_missing_timecode";
   private static final String TYPICAL_MISSING_SEQUENCE = "subrip/typical_missing_sequence";
@@ -52,6 +53,16 @@ public final class SubripParserTest extends InstrumentationTestCase {
     assertTypicalCue3(subtitle, 4);
   }
 
+  public void testParseTypicalWithByteOrderMark() throws IOException {
+    SubripParser parser = new SubripParser();
+    byte[] bytes = TestUtil.getByteArray(getInstrumentation(), TYPICAL_WITH_BYTE_ORDER_MARK);
+    SubripSubtitle subtitle = parser.parse(bytes, 0, bytes.length);
+    assertEquals(6, subtitle.getEventTimeCount());
+    assertTypicalCue1(subtitle, 0);
+    assertTypicalCue2(subtitle, 2);
+    assertTypicalCue3(subtitle, 4);
+  }
+
   public void testParseTypicalExtraBlankLine() throws IOException {
     SubripParser parser = new SubripParser();
     byte[] bytes = TestUtil.getByteArray(getInstrumentation(), TYPICAL_EXTRA_BLANK_LINE);

library/src/androidTest/java/com/google/android/exoplayer/util/ParsableByteArrayTest.java

@@ -346,9 +346,9 @@ public class ParsableByteArrayTest extends TestCase {
     assertNull(parser.readLine());
   }
 
-  public void testReadTwoLinesWithLfFollowedByCr() {
+  public void testReadTwoLinesWithCrFollowedByLf() {
     byte[] bytes = new byte[] {
-      'f', 'o', 'o', '\n', '\r', 'b', 'a', 'r'
+      'f', 'o', 'o', '\r', '\n', 'b', 'a', 'r'
     };
     ParsableByteArray parser = new ParsableByteArray(bytes);
     assertEquals("foo", parser.readLine());
@@ -358,7 +358,7 @@ public class ParsableByteArrayTest extends TestCase {
 
   public void testReadThreeLinesWithEmptyLine() {
     byte[] bytes = new byte[] {
-      'f', 'o', 'o', '\n', '\r', '\n', 'b', 'a', 'r'
+      'f', 'o', 'o', '\r', '\n', '\r', 'b', 'a', 'r'
     };
     ParsableByteArray parser = new ParsableByteArray(bytes);
     assertEquals("foo", parser.readLine());
@@ -367,9 +367,9 @@ public class ParsableByteArrayTest extends TestCase {
     assertNull(parser.readLine());
   }
 
-  public void testReadFourLinesWithCrFollowedByLf() {
+  public void testReadFourLinesWithLfFollowedByCr() {
     byte[] bytes = new byte[] {
-      'f', 'o', 'o', '\r', '\n', '\n', 'b', 'a', 'r', '\n', '\r'
+      'f', 'o', 'o', '\n', '\r', '\r', 'b', 'a', 'r', '\r', '\n'
     };
     ParsableByteArray parser = new ParsableByteArray(bytes);
     assertEquals("foo", parser.readLine());

library/src/main/java/com/google/android/exoplayer/util/ParsableByteArray.java

@@ -307,12 +307,14 @@ public final class ParsableByteArray {
   }
 
   /**
-   * Reads a line of text. A line is considered to be terminated by any one of a line feed ('\n'), a
+   * Reads a line of text.
-   * carriage return ('\r'), or a carriage return followed immediately by a line feed. Platform
+   * <p>
-   * default's charset used.
+   * A line is considered to be terminated by any one of a carriage return ('\r'), a line feed
+   * ('\n'), or a carriage return followed immediately by a line feed ('\r\n'). The system's default
+   * charset (UTF-8) is used.
    *
    * @return A String containing the contents of the line, not including any line-termination
-   *    characters, or null if the end of the stream has been reached.
+   *     characters, or null if the end of the stream has been reached.
    */
   public String readLine() {
     if (bytesLeft() == 0) {
@@ -322,18 +324,23 @@ public final class ParsableByteArray {
     while (lineLimit < limit && data[lineLimit] != '\n' && data[lineLimit] != '\r') {
       lineLimit++;
     }
+    if (lineLimit - position >= 3 && data[position] == (byte) 0xEF
+        && data[position + 1] == (byte) 0xBB && data[position + 2] == (byte) 0xBF) {
+      // There's a byte order mark at the start of the line. Discard it.
+      position += 3;
+    }
     String line = new String(data, position, lineLimit - position);
     position = lineLimit;
     if (position == limit) {
       return line;
     }
-    if (data[position] == '\n') {
+    if (data[position] == '\r') {
       position++;
       if (position == limit) {
         return line;
       }
     }
-    if (data[position] == '\r') {
+    if (data[position] == '\n') {
       position++;
     }
     return line;