Expose cue settings parser

This CL exposes the cue settings parser in order to allow its usage from the MP4Webvtt extractor. Also fixes a few mistakes from the previous related CL.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112145806

library/src/main/java/com/google/android/exoplayer/text/webvtt/WebvttCue.java

@@ -18,6 +18,7 @@ package com.google.android.exoplayer.text.webvtt;
 import com.google.android.exoplayer.text.Cue;
 
 import android.text.Layout.Alignment;
+import android.util.Log;
 
 /**
  * A representation of a WebVTT cue.
@@ -53,4 +54,127 @@ import android.text.Layout.Alignment;
     return (line == DIMEN_UNSET && position == DIMEN_UNSET);
   }
 
+  /**
+   * Builder for WebVTT cues.
+   */
+  @SuppressWarnings("hiding")
+  public static final class Builder {
+
+    private static final String TAG = "WebvttCueBuilder";
+
+    private long startTime;
+    private long endTime;
+    private CharSequence text;
+    private Alignment textAlignment;
+    private float line;
+    private int lineType;
+    private int lineAnchor;
+    private float position;
+    private int positionAnchor;
+    private float width;
+
+    // Initialization methods
+
+    public Builder() {
+      reset();
+    }
+
+    public void reset() {
+      startTime = 0;
+      endTime = 0;
+      text = null;
+      textAlignment = null;
+      line = Cue.DIMEN_UNSET;
+      lineType = Cue.TYPE_UNSET;
+      lineAnchor = Cue.TYPE_UNSET;
+      position = Cue.DIMEN_UNSET;
+      positionAnchor = Cue.TYPE_UNSET;
+      width = Cue.DIMEN_UNSET;
+    }
+
+    // Construction methods
+
+    public WebvttCue build() {
+      if (position != Cue.DIMEN_UNSET && positionAnchor == Cue.TYPE_UNSET) {
+        derivePositionAnchorFromAlignment();
+      }
+      return new WebvttCue(startTime, endTime, text, textAlignment, line, lineType, lineAnchor,
+          position, positionAnchor, width);
+    }
+
+    public Builder setStartTime(long time) {
+      startTime = time;
+      return this;
+    }
+
+    public Builder setEndTime(long time) {
+      endTime = time;
+      return this;
+    }
+
+    public Builder setText(CharSequence aText) {
+      text = aText;
+      return this;
+    }
+
+    public Builder setTextAlignment(Alignment textAlignment) {
+      this.textAlignment = textAlignment;
+      return this;
+    }
+
+    public Builder setLine(float line) {
+      this.line = line;
+      return this;
+    }
+
+    public Builder setLineType(int lineType) {
+      this.lineType = lineType;
+      return this;
+    }
+
+    public Builder setLineAnchor(int lineAnchor) {
+      this.lineAnchor = lineAnchor;
+      return this;
+    }
+
+    public Builder setPosition(float position) {
+      this.position = position;
+      return this;
+    }
+
+    public Builder setPositionAnchor(int positionAnchor) {
+      this.positionAnchor = positionAnchor;
+      return this;
+    }
+
+    public Builder setWidth(float width) {
+      this.width = width;
+      return this;
+    }
+
+    private Builder derivePositionAnchorFromAlignment() {
+      if (textAlignment == null) {
+        positionAnchor = Cue.TYPE_UNSET;
+      } else {
+        switch (textAlignment) {
+          case ALIGN_NORMAL:
+            positionAnchor = Cue.ANCHOR_TYPE_START;
+            break;
+          case ALIGN_CENTER:
+            positionAnchor = Cue.ANCHOR_TYPE_MIDDLE;
+            break;
+          case ALIGN_OPPOSITE:
+            positionAnchor = Cue.ANCHOR_TYPE_END;
+            break;
+          default:
+            Log.w(TAG, "Unrecognized alignment: " + textAlignment);
+            positionAnchor = Cue.ANCHOR_TYPE_START;
+            break;
+        }
+      }
+      return this;
+    }
+
+  }
+
 }

library/src/main/java/com/google/android/exoplayer/text/webvtt/WebvttParser.java

@@ -33,10 +33,12 @@ public final class WebvttParser implements SubtitleParser {
 
   private final WebvttCueParser cueParser;
   private final ParsableByteArray parsableWebvttData;
+  private final WebvttCue.Builder webvttCueBuilder;
 
   public WebvttParser() {
     cueParser = new WebvttCueParser();
     parsableWebvttData = new ParsableByteArray();
+    webvttCueBuilder = new WebvttCue.Builder();
   }
 
   @Override
@@ -48,6 +50,7 @@ public final class WebvttParser implements SubtitleParser {
   public final WebvttSubtitle parse(byte[] bytes, int offset, int length) throws ParserException {
     parsableWebvttData.reset(bytes, offset + length);
     parsableWebvttData.setPosition(offset);
+    webvttCueBuilder.reset(); // In case a previous parse run failed with a ParserException.
 
     // Validate the first line of the header, and skip the remainder.
     WebvttParserUtil.validateWebvttHeaderLine(parsableWebvttData);
@@ -55,9 +58,9 @@ public final class WebvttParser implements SubtitleParser {
 
     // Extract Cues
     ArrayList<WebvttCue> subtitles = new ArrayList<>();
-    WebvttCue currentWebvttCue;
-    while ((currentWebvttCue = cueParser.parseNextValidCue(parsableWebvttData)) != null) {
-      subtitles.add(currentWebvttCue);
+    while (cueParser.parseNextValidCue(parsableWebvttData, webvttCueBuilder)) {
+      subtitles.add(webvttCueBuilder.build());
+      webvttCueBuilder.reset();
     }
     return new WebvttSubtitle(subtitles);
   }