Add DashDownloadActionTest

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=169522830

library/dash/build.gradle

@@ -39,6 +39,11 @@ dependencies {
     androidTestCompile 'com.google.dexmaker:dexmaker:' + dexmakerVersion
     androidTestCompile 'com.google.dexmaker:dexmaker-mockito:' + dexmakerVersion
     androidTestCompile 'org.mockito:mockito-core:' + mockitoVersion
+    testCompile project(modulePrefix + 'testutils')
+    testCompile 'com.google.truth:truth:' + truthVersion
+    testCompile 'junit:junit:' + junitVersion
+    testCompile 'org.mockito:mockito-core:' + mockitoVersion
+    testCompile 'org.robolectric:robolectric:' + robolectricVersion
 }
 
 ext {

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

@@ -80,4 +80,27 @@ public int compareTo(@NonNull RepresentationKey o) {
     return result;
   }
 
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) {
+      return true;
+    }
+    if (o == null || getClass() != o.getClass()) {
+      return false;
+    }
+
+    RepresentationKey that = (RepresentationKey) o;
+    return periodIndex == that.periodIndex
+        && adaptationSetIndex == that.adaptationSetIndex
+        && representationIndex == that.representationIndex;
+  }
+
+  @Override
+  public int hashCode() {
+    int result = periodIndex;
+    result = 31 * result + adaptationSetIndex;
+    result = 31 * result + representationIndex;
+    return result;
+  }
+
 }