Only update codecInfo when needed

This avoids calling getDecoderInfo repeatedly in the case
where shouldInitCodec return false (e.g. because we don't
have a surface and cannot instantiate a dummy surface).

Issue: #677

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=157847702

library/core/src/main/java/com/google/android/exoplayer2/mediacodec/MediaCodecRenderer.java

@@ -314,14 +314,14 @@ public abstract class MediaCodecRenderer extends BaseRenderer {
       }
     }
 
-    MediaCodecInfo codecInfo = null;
+    if (codecInfo == null) {
       try {
         codecInfo = getDecoderInfo(mediaCodecSelector, format, drmSessionRequiresSecureDecoder);
         if (codecInfo == null && drmSessionRequiresSecureDecoder) {
-        // The drm session indicates that a secure decoder is required, but the device does not have
+          // The drm session indicates that a secure decoder is required, but the device does not
-        // one. Assuming that supportsFormat indicated support for the media being played, we know
+          // have one. Assuming that supportsFormat indicated support for the media being played, we
-        // that it does not require a secure output path. Most CDM implementations allow playback to
+          // know that it does not require a secure output path. Most CDM implementations allow
-        // proceed with a non-secure decoder in this case, so we try our luck.
+          // playback to proceed with a non-secure decoder in this case, so we try our luck.
           codecInfo = getDecoderInfo(mediaCodecSelector, format, false);
           if (codecInfo != null) {
             Log.w(TAG, "Drm session requires secure decoder for " + mimeType + ", but "
@@ -338,12 +338,12 @@ public abstract class MediaCodecRenderer extends BaseRenderer {
             drmSessionRequiresSecureDecoder,
             DecoderInitializationException.NO_SUITABLE_DECODER_ERROR));
       }
+    }
 
     if (!shouldInitCodec(codecInfo)) {
       return;
     }
 
-    this.codecInfo = codecInfo;
     String codecName = codecInfo.name;
     codecNeedsDiscardToSpsWorkaround = codecNeedsDiscardToSpsWorkaround(codecName, format);
     codecNeedsFlushWorkaround = codecNeedsFlushWorkaround(codecName);

library/core/src/main/java/com/google/android/exoplayer2/mediacodec/MediaCodecSelector.java

@@ -55,8 +55,7 @@ public interface MediaCodecSelector {
   /**
    * Selects a decoder to instantiate for audio passthrough.
    *
-   * @return A {@link MediaCodecInfo} describing the decoder, or null if no suitable decoder
+   * @return A {@link MediaCodecInfo} describing the decoder, or null if no suitable decoder exists.
-   *     exists.
    * @throws DecoderQueryException Thrown if there was an error querying decoders.
    */
   MediaCodecInfo getPassthroughDecoderInfo() throws DecoderQueryException;

library/core/src/main/java/com/google/android/exoplayer2/mediacodec/MediaCodecUtil.java

@@ -99,7 +99,7 @@ public final class MediaCodecUtil {
 
   /**
    * Returns information about a decoder suitable for audio passthrough.
-   **
+   *
    * @return A {@link MediaCodecInfo} describing the decoder, or null if no suitable decoder
    *     exists.
    */