ok, basic tracing support

This doesn't do anything in the default process-per-task mode, because
those child tasks exit using _exit(), which doesn't trigger the event
tracer destructor to flush.

I don't remember exactly why I exit with _exit(), so I'm going to have
to follow up on that.  But written this way as I think I'm at least
initializing the tracing in the right place for each process for the
future.

In threaded (-j -1) and serial (-j 0) modes, everything seems to work
great.

I'm also thinking I might add a tracer like the SkDebugf tracer but
using ok_log(), which handles interlaced logging from concurrent tasks
better than vanilla SkDebugf.

Example:
    ninja -C out ok; and out/ok gm 8888 filter:search=fontmgr_bounds trace -j -1

Change-Id: Ia3cdad930ce65e6fd12fa74f3fb00894e35138d3
Reviewed-on: https://skia-review.googlesource.com/26350
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>

1 files changed, 6 insertions, 4 deletions

diff --git a/tools/trace/SkEventTracingPriv.cpp b/tools/trace/SkEventTracingPriv.cpp
index 783cfeaa32..42d992cb13 100644
--- a/tools/trace/SkEventTracingPriv.cpp
+++ b/tools/trace/SkEventTracingPriv.cpp
@@ -22,12 +22,14 @@ DEFINE_string(trace, "",
               "               trace events to specified file as JSON, for viewing\n"
               "               with chrome://tracing");
 
-void initializeEventTracingForTools() {
-    if (FLAGS_trace.isEmpty()) {
-        return;
+void initializeEventTracingForTools(const char* traceFlag) {
+    if (!traceFlag) {
+        if (FLAGS_trace.isEmpty()) {
+            return;
+        }
+        traceFlag = FLAGS_trace[0];
     }
 
-    const char* traceFlag = FLAGS_trace[0];
     SkEventTracer* eventTracer = nullptr;
     if (0 == strcmp(traceFlag, "atrace")) {
         eventTracer = new SkATrace();