Add config to enable snapshot preloading

Enable preloading if config_enableTaskSnapshotPreloading instead of
assuming it should be off for all low ram devices. This allows it to be
configured via an overlay.

Test: TaskSnapshotCacheTest
Test: TaskSnapshotControllerTest
Test: TaskSnapshotPersisterLoaderTest
Test: TaskSnapshotSurfaceTest
Bug: 148099851
Change-Id: I9e3320dcff5b710e110cc7199c41c5a004991592

quickstep/src/com/android/quickstep/TaskThumbnailCache.java

@@ -43,6 +43,7 @@ public class TaskThumbnailCache {
     private final int mCacheSize;
     private final TaskKeyLruCache<ThumbnailData> mCache;
     private final HighResLoadingState mHighResLoadingState;
+    private final boolean mEnableTaskSnapshotPreloading;
 
     public static class HighResLoadingState {
         private boolean mIsLowRamDevice;
@@ -100,6 +101,7 @@ public class TaskThumbnailCache {
 
         Resources res = context.getResources();
         mCacheSize = res.getInteger(R.integer.recentsThumbnailCacheSize);
+        mEnableTaskSnapshotPreloading = res.getBoolean(R.bool.config_enableTaskSnapshotPreloading);
         mCache = new TaskKeyLruCache<>(mCacheSize);
     }
 
@@ -212,7 +214,7 @@ public class TaskThumbnailCache {
      * @return Whether to enable background preloading of task thumbnails.
      */
     public boolean isPreloadingEnabled() {
-        return !mHighResLoadingState.mIsLowRamDevice && mHighResLoadingState.mVisible;
+        return mEnableTaskSnapshotPreloading && mHighResLoadingState.mVisible;
     }
 
     public static abstract class ThumbnailLoadRequest extends HandlerRunnable {

res/values/config.xml

@@ -117,6 +117,9 @@
     <!-- Recents -->
     <item type="id" name="overview_panel"/>
 
+    <!-- Whether to enable background preloading of task thumbnails. -->
+    <bool name="config_enableTaskSnapshotPreloading">true</bool>
+
     <!-- Configuration resources -->
     <array name="dynamic_resources"> </array>
 </resources>