Prepare code to allow image decoder to be reused

This change refactors ImageDecoder to prepare it for reuse
for multi-slice decoding. There is no functional change.

bug: 78475896

Test: CTS MediaMetadataRetrieverTest;
Manual test of HEIF image decoding and thumbnail extraction.

Change-Id: I8c16042020c7db3d3714d22322e6304ea4192e33
diff --git a/media/libmediaplayerservice/MetadataRetrieverClient.cpp b/media/libmediaplayerservice/MetadataRetrieverClient.cpp
index 672b832..fa41c06 100644
--- a/media/libmediaplayerservice/MetadataRetrieverClient.cpp
+++ b/media/libmediaplayerservice/MetadataRetrieverClient.cpp
@@ -48,7 +48,6 @@
 {
     ALOGV("MetadataRetrieverClient constructor pid(%d)", pid);
     mPid = pid;
-    mThumbnail = NULL;
     mAlbumArt = NULL;
     mRetriever = NULL;
 }
@@ -77,7 +76,6 @@
     ALOGV("disconnect from pid %d", mPid);
     Mutex::Autolock lock(mLock);
     mRetriever.clear();
-    mThumbnail.clear();
     mAlbumArt.clear();
     IPCThreadState::self()->flushCommands();
 }
@@ -201,7 +199,6 @@
             (long long)timeUs, option, colorFormat, metaOnly);
     Mutex::Autolock lock(mLock);
     Mutex::Autolock glock(sLock);
-    mThumbnail.clear();
     if (mRetriever == NULL) {
         ALOGE("retriever is not initialized");
         return NULL;
@@ -220,7 +217,6 @@
             index, colorFormat, metaOnly, thumbnail);
     Mutex::Autolock lock(mLock);
     Mutex::Autolock glock(sLock);
-    mThumbnail.clear();
     if (mRetriever == NULL) {
         ALOGE("retriever is not initialized");
         return NULL;
diff --git a/media/libmediaplayerservice/MetadataRetrieverClient.h b/media/libmediaplayerservice/MetadataRetrieverClient.h
index e774c8f..63ba44a 100644
--- a/media/libmediaplayerservice/MetadataRetrieverClient.h
+++ b/media/libmediaplayerservice/MetadataRetrieverClient.h
@@ -73,9 +73,8 @@
     sp<MediaMetadataRetrieverBase>         mRetriever;
     pid_t                                  mPid;
 
-    // Keep the shared memory copy of album art and capture frame (for thumbnail)
+    // Keep the shared memory copy of album art
     sp<IMemory>                            mAlbumArt;
-    sp<IMemory>                            mThumbnail;
 };
 
 }; // namespace android