Tracing work

* Fix: `E` events need to have the same information that is on the
  corresponding `B` events.  (Superseded below.)

* Use `I` (not `i`) for instant events, so they show in devtools
  too.  (Though they don't go through the flame chart as they do in
  `about://tracing`, so they're not nearly as useful.)

* Abstract the code that writes the records in a single `writeEvent`
  local function.

* Make `args` optional, and default to `undefined` (which will not add
  them) at all.

* Drop the `{ "ts": ... }` wrapper around the `args`, after verifying
  that having arguments with names like `begin`, `end`, `pos`, `id`
  doesn't interfere with either UIs.

* Add `tracing.push`/`tracing.pop` for complete events, change a few
  `.begin`/`.end` to use these.  (The caveat is that until there's an exit
  handler to dump unterminated events, these won't show in the dump.  When
  that's done the push/pop variant can be used everywhere.)

* Add meta lines to name the process and the thread, and a line that
  avoids the warning when opening in devtools.

src/compiler/program.ts

@@ -780,7 +780,8 @@ namespace ts {
         // Track source files that are source files found by searching under node_modules, as these shouldn't be compiled.
         const sourceFilesFoundSearchingNodeModules = new Map<string, boolean>();
 
-        tracing.begin(tracing.Phase.Program, "createProgram", {});
+        const tracingData: tracing.EventData = [tracing.Phase.Program, "createProgram"];
+        tracing.begin(...tracingData);
         performance.mark("beforeProgram");
 
         const host = createProgramOptions.host || createCompilerHost(options);
@@ -1032,7 +1033,7 @@ namespace ts {
         verifyCompilerOptions();
         performance.mark("afterProgram");
         performance.measure("Program", "beforeProgram", "afterProgram");
-        tracing.end();
+        tracing.end(...tracingData);
 
         return program;
 
@@ -1590,7 +1591,8 @@ namespace ts {
 
         function emitBuildInfo(writeFileCallback?: WriteFileCallback): EmitResult {
             Debug.assert(!outFile(options));
-            tracing.begin(tracing.Phase.Emit, "emitBuildInfo", {});
+            const tracingData: tracing.EventData = [tracing.Phase.Emit, "emitBuildInfo"];
+            tracing.begin(...tracingData);
             performance.mark("beforeEmit");
             const emitResult = emitFiles(
                 notImplementedResolver,
@@ -1603,7 +1605,7 @@ namespace ts {
 
             performance.mark("afterEmit");
             performance.measure("Emit", "beforeEmit", "afterEmit");
-            tracing.end();
+            tracing.end(...tracingData);
             return emitResult;
         }
 
@@ -1664,9 +1666,10 @@ namespace ts {
         }
 
         function emit(sourceFile?: SourceFile, writeFileCallback?: WriteFileCallback, cancellationToken?: CancellationToken, emitOnlyDtsFiles?: boolean, transformers?: CustomTransformers, forceDtsEmit?: boolean): EmitResult {
-            tracing.begin(tracing.Phase.Emit, "emit", { path: sourceFile?.path });
+            const tracingData: tracing.EventData = [tracing.Phase.Emit, "emit", { path: sourceFile?.path }];
+            tracing.begin(...tracingData);
             const result = runWithCancellationToken(() => emitWorker(program, sourceFile, writeFileCallback, cancellationToken, emitOnlyDtsFiles, transformers, forceDtsEmit));
-            tracing.end();
+            tracing.end(...tracingData);
             return result;
         }