Fix DashManifestParser to properly skip unknown tags

Robustness fix to make sure we ignore tags with known names, but
which are nested inside of unknown tags. For example we don't want
to parse the third period in:

<Period>...</Period>
<Period>...</Period>
<CustomTag>
  <Period>...</Period>
</CustomTag>

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=217101630

library/dash/src/main/java/com/google/android/exoplayer2/source/dash/manifest/DashManifestParser.java

@@ -155,6 +155,8 @@ public class DashManifestParser extends DefaultHandler
               : (period.startMs + periodDurationMs);
           periods.add(period);
         }
+      } else {
+        maybeSkipTag(xpp);
       }
     } while (!XmlPullParserUtil.isEndTag(xpp, "MPD"));
 
@@ -221,6 +223,8 @@ public class DashManifestParser extends DefaultHandler
         segmentBase = parseSegmentList(xpp, null);
       } else if (XmlPullParserUtil.isStartTag(xpp, "SegmentTemplate")) {
         segmentBase = parseSegmentTemplate(xpp, null);
+      } else {
+        maybeSkipTag(xpp);
       }
     } while (!XmlPullParserUtil.isEndTag(xpp, "Period"));
 
@@ -409,8 +413,8 @@ public class DashManifestParser extends DefaultHandler
       } else if (XmlPullParserUtil.isStartTag(xpp, "widevine:license")) {
         String robustnessLevel = xpp.getAttributeValue(null, "robustness_level");
         requiresSecureDecoder = robustnessLevel != null && robustnessLevel.startsWith("HW");
-      } else if (data == null) {
+      } else if (data == null
-        if (XmlPullParserUtil.isStartTagIgnorePrefix(xpp, "pssh")
+          && XmlPullParserUtil.isStartTagIgnorePrefix(xpp, "pssh")
           && xpp.next() == XmlPullParser.TEXT) {
         // The cenc:pssh element is defined in 23001-7:2015.
         data = Base64.decode(xpp.getText(), Base64.DEFAULT);
@@ -419,12 +423,16 @@ public class DashManifestParser extends DefaultHandler
           Log.w(TAG, "Skipping malformed cenc:pssh data");
           data = null;
         }
-        } else if (C.PLAYREADY_UUID.equals(uuid) && XmlPullParserUtil.isStartTag(xpp, "mspr:pro")
+      } else if (data == null
+          && C.PLAYREADY_UUID.equals(uuid)
+          && XmlPullParserUtil.isStartTag(xpp, "mspr:pro")
           && xpp.next() == XmlPullParser.TEXT) {
         // The mspr:pro element is defined in DASH Content Protection using Microsoft PlayReady.
-          data = PsshAtomUtil.buildPsshAtom(C.PLAYREADY_UUID,
+        data =
-              Base64.decode(xpp.getText(), Base64.DEFAULT));
+            PsshAtomUtil.buildPsshAtom(
-        }
+                C.PLAYREADY_UUID, Base64.decode(xpp.getText(), Base64.DEFAULT));
+      } else {
+        maybeSkipTag(xpp);
       }
     } while (!XmlPullParserUtil.isEndTag(xpp, "ContentProtection"));
     SchemeData schemeData =
@@ -462,7 +470,7 @@ public class DashManifestParser extends DefaultHandler
    */
   protected void parseAdaptationSetChild(XmlPullParser xpp)
       throws XmlPullParserException, IOException {
-    // pass
+    maybeSkipTag(xpp);
   }
 
   // Representation parsing.
@@ -526,6 +534,8 @@ public class DashManifestParser extends DefaultHandler
         inbandEventStreams.add(parseDescriptor(xpp, "InbandEventStream"));
       } else if (XmlPullParserUtil.isStartTag(xpp, "SupplementalProperty")) {
         supplementalProperties.add(parseDescriptor(xpp, "SupplementalProperty"));
+      } else {
+        maybeSkipTag(xpp);
       }
     } while (!XmlPullParserUtil.isEndTag(xpp, "Representation"));
 
@@ -664,6 +674,8 @@ public class DashManifestParser extends DefaultHandler
       xpp.next();
       if (XmlPullParserUtil.isStartTag(xpp, "Initialization")) {
         initialization = parseInitialization(xpp);
+      } else {
+        maybeSkipTag(xpp);
       }
     } while (!XmlPullParserUtil.isEndTag(xpp, "SegmentBase"));
 
@@ -701,6 +713,8 @@ public class DashManifestParser extends DefaultHandler
           segments = new ArrayList<>();
         }
         segments.add(parseSegmentUrl(xpp));
+      } else {
+        maybeSkipTag(xpp);
       }
     } while (!XmlPullParserUtil.isEndTag(xpp, "SegmentList"));
 
@@ -747,6 +761,8 @@ public class DashManifestParser extends DefaultHandler
         initialization = parseInitialization(xpp);
       } else if (XmlPullParserUtil.isStartTag(xpp, "SegmentTimeline")) {
         timeline = parseSegmentTimeline(xpp);
+      } else {
+        maybeSkipTag(xpp);
       }
     } while (!XmlPullParserUtil.isEndTag(xpp, "SegmentTemplate"));
 
@@ -794,6 +810,8 @@ public class DashManifestParser extends DefaultHandler
         EventMessage event = parseEvent(xpp, schemeIdUri, value, timescale,
             scratchOutputStream);
         eventMessages.add(event);
+      } else {
+        maybeSkipTag(xpp);
       }
     } while (!XmlPullParserUtil.isEndTag(xpp, "EventStream"));
 
@@ -932,6 +950,8 @@ public class DashManifestParser extends DefaultHandler
           segmentTimeline.add(buildSegmentTimelineElement(elapsedTime, duration));
           elapsedTime += duration;
         }
+      } else {
+        maybeSkipTag(xpp);
       }
     } while (!XmlPullParserUtil.isEndTag(xpp, "SegmentTimeline"));
     return segmentTimeline;
@@ -995,6 +1015,29 @@ public class DashManifestParser extends DefaultHandler
 
   // Utility methods.
 
+  /**
+   * If the provided {@link XmlPullParser} is currently positioned at the start of a tag, skips
+   * forward to the end of that tag.
+   *
+   * @param xpp The {@link XmlPullParser}.
+   * @throws XmlPullParserException If an error occurs parsing the stream.
+   * @throws IOException If an error occurs reading the stream.
+   */
+  public static void maybeSkipTag(XmlPullParser xpp) throws IOException, XmlPullParserException {
+    if (!XmlPullParserUtil.isStartTag(xpp)) {
+      return;
+    }
+    int depth = 1;
+    while (depth != 0) {
+      xpp.next();
+      if (XmlPullParserUtil.isStartTag(xpp)) {
+        depth++;
+      } else if (XmlPullParserUtil.isEndTag(xpp)) {
+        depth--;
+      }
+    }
+  }
+
   /**
    * Removes unnecessary {@link SchemeData}s with null {@link SchemeData#data}.
    */