Reuse frame decoder for sequential frame retrievel

Allow sequential frame retrieval to reuse the decoder without
re-init and re-seek.

Get rid of IMediaMetadataRetriever api that retrieves multiple
frames at a time, this method could hold up more memory than
what's needed, because the client side has to copy the frames
to a separate set of bitmaps anyways.

This change is needed to support animation Drawbles efficiently
which typically get one frame at a time.

bug: 120414514
test: cts MediaMetadataRetrieverTest, local tests that tests MetadataRetriever thumbnails

Change-Id: I09924408b51bc7491fc5dee121dce9a286c5911f
diff --git a/media/libmedia/mediametadataretriever.cpp b/media/libmedia/mediametadataretriever.cpp
index e61b04d..2ae76b3 100644
--- a/media/libmedia/mediametadataretriever.cpp
+++ b/media/libmedia/mediametadataretriever.cpp
@@ -179,18 +179,16 @@
             index, colorFormat, left, top, right, bottom);
 }
 
-status_t MediaMetadataRetriever::getFrameAtIndex(
-        std::vector<sp<IMemory> > *frames,
-        int frameIndex, int numFrames, int colorFormat, bool metaOnly) {
-    ALOGV("getFrameAtIndex: frameIndex(%d), numFrames(%d), colorFormat(%d) metaOnly(%d)",
-            frameIndex, numFrames, colorFormat, metaOnly);
+sp<IMemory>  MediaMetadataRetriever::getFrameAtIndex(
+        int index, int colorFormat, bool metaOnly) {
+    ALOGV("getFrameAtIndex: index(%d), colorFormat(%d) metaOnly(%d)",
+            index, colorFormat, metaOnly);
     Mutex::Autolock _l(mLock);
     if (mRetriever == 0) {
         ALOGE("retriever is not initialized");
-        return INVALID_OPERATION;
+        return NULL;
     }
-    return mRetriever->getFrameAtIndex(
-            frames, frameIndex, numFrames, colorFormat, metaOnly);
+    return mRetriever->getFrameAtIndex(index, colorFormat, metaOnly);
 }
 
 const char* MediaMetadataRetriever::extractMetadata(int keyCode)