hwui: change TRIM_COMPLETE to TRIM_BACKGROUND

In preparation for lifecycle-consistent TRIM_MEMORY callbacks, be more
aggressive with TRIM_BACKGROUND.

Test: android.platform.test.scenario.launcher.FlingAllAppsMicrobenchmark
Bug: 253914117
Change-Id: I4c8b3331312f198dbf3f74495b8412873d1ca302

libs/hwui/renderthread/CacheManager.cpp

@@ -117,12 +117,8 @@ void CacheManager::trimMemory(TrimLevel mode) {
     // flush and submit all work to the gpu and wait for it to finish
     mGrContext->flushAndSubmit(/*syncCpu=*/true);
 
-    if (!Properties::isHighEndGfx && mode >= TrimLevel::MODERATE) {
-        mode = TrimLevel::COMPLETE;
-    }
-
     switch (mode) {
-        case TrimLevel::COMPLETE:
+        case TrimLevel::BACKGROUND:
             mGrContext->freeGpuResources();
             SkGraphics::PurgeAllCaches();
             mRenderThread.destroyRenderingContext();