[VM/Timeline] Update CLI options to make it clearer that the Perfetto file recorder records to a file

TEST=Manually verified that the modified CLI options worked as expected, CI

Change-Id: Ibaa308e5c9c3b96c939e2007ee2eaaca30eae280
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/288063
Reviewed-by: Ben Konyi <bkonyi@google.com>

pkg/dartdev/lib/src/commands/run.dart

@@ -133,7 +133,7 @@ class RunCommand extends DartdevCommand {
         ..addOption('timeline-recorder',
             help: 'Selects the timeline recorder to use.\n'
                 'Valid recorders include: none, ring, endless, startup, '
-                'systrace, file, callback.\n'
+                'systrace, file, callback, perfettofile.\n'
                 'Defaults to ring.',
             valueHelp: 'recorder');
     } else {

pkg/vm_service/lib/src/vm_service.dart

@@ -941,10 +941,10 @@ abstract class VmServiceInterface {
   /// timeline request`, will be returned as timeline events are handled by the
   /// OS in these modes.
   ///
-  /// If `getVMTimeline` is invoked while the current recorder is File, an
-  /// [RPCError] with error code `114`, `invalid timeline request`, will be
-  /// returned as timeline events are written directly to a file, and thus
-  /// cannot be retrieved through the VM Service, in this mode.
+  /// If `getVMTimeline` is invoked while the current recorder is File or
+  /// Perfettofile, an [RPCError] with error code `114`, `invalid timeline
+  /// request`, will be returned as timeline events are written directly to a
+  /// file, and thus cannot be retrieved through the VM Service, in these modes.
   Future<Timeline> getVMTimeline(
       {int? timeOriginMicros, int? timeExtentMicros});
 
@@ -4735,7 +4735,7 @@ class Flag {
 
   /// The value of this flag as a string.
   ///
-  /// If this property is absent, then the value of the flag was NULL.
+  /// If this property is absent, then the value of the flag was nullptr.
   @optional
   String? valueAsString;
 

runtime/vm/service.cc

@@ -4186,7 +4186,8 @@ static void GetVMTimeline(Thread* thread, JSONStream* js) {
         "for this recorder type.",
         timeline_recorder->name());
     return;
-  } else if (strcmp(name, FILE_RECORDER_NAME) == 0) {
+  } else if (strcmp(name, FILE_RECORDER_NAME) == 0 ||
+             strcmp(name, PERFETTO_FILE_RECORDER_NAME) == 0) {
     js->PrintError(kInvalidTimelineRequest,
                    "A recorder of type \"%s\" is currently in use. As a "
                    "result, timeline events are written directly to a file and "

runtime/vm/service/service.md

@@ -1214,10 +1214,11 @@ Macos or Systrace, an [RPC error](#rpc-error) with error code _114_,
 `invalid timeline request`, will be returned as timeline events are handled by
 the OS in these modes.
 
-If _getVMTimeline_ is invoked while the current recorder is File, an
-[RPC error](#rpc-error) with error code _114_, `invalid timeline request`, will
-be returned as timeline events are written directly to a file, and thus cannot
-be retrieved through the VM Service, in this mode.
+If _getVMTimeline_ is invoked while the current recorder is File or
+Perfettofile, an [RPC error](#rpc-error) with error code _114_,
+`invalid timeline request`, will be returned as timeline events are written
+directly to a file, and thus cannot be retrieved through the VM Service, in
+these modes.
 
 ### getVMTimelineFlags
 

runtime/vm/timeline.cc

@@ -110,7 +110,7 @@ GetProtoPreamble(const intptr_t size) {
 #define DEFAULT_TIMELINE_RECORDER "ring"
 #if defined(SUPPORT_PERFETTO)
 #define SUPPORTED_TIMELINE_RECORDERS                                           \
-  "ring, endless, startup, systrace, file, callback, perfetto"
+  "ring, endless, startup, systrace, file, callback, perfettofile"
 #else
 #define SUPPORTED_TIMELINE_RECORDERS                                           \
   "ring, endless, startup, systrace, file, callback"
@@ -249,14 +249,13 @@ static TimelineEventRecorder* CreateTimelineRecorder() {
   // The Perfetto file recorder is disabled in PRODUCT mode to avoid the large
   // binary size increase that it brings.
   {
-    const intptr_t kLengthOfWordPerfetto = 8;
-    if (Utils::StrStartsWith(flag, "perfetto") &&
-        (flag[kLengthOfWordPerfetto] == '\0' ||
-         flag[kLengthOfWordPerfetto] == ':' ||
-         flag[kLengthOfWordPerfetto] == '=')) {
-      const char* filename = flag[kLengthOfWordPerfetto] == '\0'
+    const intptr_t kPrefixLength = 12;
+    if (Utils::StrStartsWith(flag, "perfettofile") &&
+        (flag[kPrefixLength] == '\0' || flag[kPrefixLength] == ':' ||
+         flag[kPrefixLength] == '=')) {
+      const char* filename = flag[kPrefixLength] == '\0'
                                  ? "dart.perfetto-trace"
-                                 : &flag[kLengthOfWordPerfetto + 1];
+                                 : &flag[kPrefixLength + 1];
       free(const_cast<char*>(FLAG_timeline_dir));
       FLAG_timeline_dir = nullptr;
       return new TimelineEventPerfettoFileRecorder(filename);

runtime/vm/timeline.h

@@ -69,7 +69,7 @@ class Zone;
 #define FILE_RECORDER_NAME "File"
 #define FUCHSIA_RECORDER_NAME "Fuchsia"
 #define MACOS_RECORDER_NAME "Macos"
-#define PERFETTO_RECORDER_NAME "Perfetto"
+#define PERFETTO_FILE_RECORDER_NAME "Perfettofile"
 #define RING_RECORDER_NAME "Ring"
 #define STARTUP_RECORDER_NAME "Startup"
 #define SYSTRACE_RECORDER_NAME "Systrace"
@@ -1249,7 +1249,7 @@ class TimelineEventPerfettoFileRecorder : public TimelineEventFileRecorderBase {
   explicit TimelineEventPerfettoFileRecorder(const char* path);
   virtual ~TimelineEventPerfettoFileRecorder();
 
-  const char* name() const final { return PERFETTO_RECORDER_NAME; }
+  const char* name() const final { return PERFETTO_FILE_RECORDER_NAME; }
 
  private:
   void WritePacket(