Rename Cache getContentMetadataSnapshot to getContentMetadata

And in ContentMetadata javadoc emphasize that it's a snapshot.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=190461436

library/core/src/main/java/com/google/android/exoplayer2/upstream/cache/Cache.java

@@ -257,10 +257,10 @@ public interface Cache {
       throws CacheException;
 
   /**
-   * Returns a snapshot of the {@link ContentMetadata} for the given key.
+   * Returns a {@link ContentMetadata} for the given key.
    *
    * @param key The cache key for the data.
-   * @return A snapshot of the {@link ContentMetadata} for the given key.
+   * @return A {@link ContentMetadata} for the given key.
    */
-  ContentMetadata getContentMetadataSnapshot(String key);
+  ContentMetadata getContentMetadata(String key);
 }

library/core/src/main/java/com/google/android/exoplayer2/upstream/cache/CachedContentIndex.java

@@ -227,8 +227,8 @@ import javax.crypto.spec.SecretKeySpec;
     cachedContent.applyMetadataMutations(mutations);
   }
 
-  /** Returns a snapshot of the {@link ContentMetadata} for the given key. */
-  public ContentMetadata getContentMetadataSnapshot(String key) {
+  /** Returns a {@link ContentMetadata} for the given key. */
+  public ContentMetadata getContentMetadata(String key) {
     CachedContent cachedContent = get(key);
     return cachedContent != null ? cachedContent.getMetadata() : DefaultContentMetadata.EMPTY;
   }

library/core/src/main/java/com/google/android/exoplayer2/upstream/cache/ContentMetadata.java

@@ -15,7 +15,7 @@
  */
 package com.google.android.exoplayer2.upstream.cache;
 
-/** Interface for accessing cached content metadata which is stored as name, value pairs. */
+/** Interface for an immutable snapshot of keyed metadata. */
 public interface ContentMetadata {
 
   /**

library/core/src/main/java/com/google/android/exoplayer2/upstream/cache/SimpleCache.java

@@ -466,7 +466,7 @@ public final class SimpleCache implements Cache {
   }
 
   @Override
-  public ContentMetadata getContentMetadataSnapshot(String key) {
-    return index.getContentMetadataSnapshot(key);
+  public ContentMetadata getContentMetadata(String key) {
+    return index.getContentMetadata(key);
   }
 }