SurfaceFlinger: Get rid of String8 in dumpsys

Test: build and gui/ui/renderengine/surfaceflinger tests and compare
dumpsys SurfaceFlinger results
Change-Id: Iafdaf73a0acbbbb8fbafc930ad86285106a07e13
diff --git a/services/surfaceflinger/TimeStats/TimeStats.cpp b/services/surfaceflinger/TimeStats/TimeStats.cpp
index 2b9f5c8..6a5488a 100644
--- a/services/surfaceflinger/TimeStats/TimeStats.cpp
+++ b/services/surfaceflinger/TimeStats/TimeStats.cpp
@@ -33,7 +33,7 @@
 namespace android {
 
 void TimeStats::parseArgs(bool asProto, const Vector<String16>& args, size_t& index,
-                          String8& result) {
+                          std::string& result) {
     ATRACE_CALL();
 
     if (args.size() > index + 10) {
@@ -564,7 +564,7 @@
     return mEnabled.load();
 }
 
-void TimeStats::dump(bool asProto, std::optional<uint32_t> maxLayers, String8& result) {
+void TimeStats::dump(bool asProto, std::optional<uint32_t> maxLayers, std::string& result) {
     ATRACE_CALL();
 
     std::lock_guard<std::mutex> lock(mMutex);
@@ -582,7 +582,7 @@
         result.append(timeStatsProto.SerializeAsString().c_str(), timeStatsProto.ByteSize());
     } else {
         ALOGD("Dumping TimeStats as text");
-        result.append(mTimeStats.toString(maxLayers).c_str());
+        result.append(mTimeStats.toString(maxLayers));
         result.append("\n");
     }
 }