First stab at JSON event tracer

Not yet thread safe (so it forces threading off).
Builds JSON on the fly, so overhead is certainly bad.
Plan to fix all of that, but this at least "works".

There is now one tracing flag: 'trace'.
- 'debugf' installs the SkDebugf tracer.
- 'atrace' installs the Android ATrace tracer.
- Any other value is interpreted as a filename, and
  produces a JSON file for chrome://tracing.

All three modes work in DM, nanobench, and Viewer.

Bug: skia:
Change-Id: I3fbc22382b99418a508c670be2770195c0a1c364
Reviewed-on: https://skia-review.googlesource.com/24781
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/tools/trace/SkEventTracingPriv.h b/tools/trace/SkEventTracingPriv.h
new file mode 100644
index 0000000000..330f3f83ed
--- /dev/null
+++ b/tools/trace/SkEventTracingPriv.h
@@ -0,0 +1,22 @@
+/*
+ * Copyright 2017 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkEventTracingPriv_DEFINED
+#define SkEventTracingPriv_DEFINED
+
+#include "SkTypes.h"
+
+/**
+ * Construct and install an SkEventTracer, based on the 'trace' command line argument.
+ *
+ * @param threadsFlag Pointer to the FLAGS_threads variable (or nullptr). This is used to disable
+ *                    threading when tracing to JSON. (Remove this param when JSON tracer is thread
+ *                    safe).
+ */
+void initializeEventTracingForTools(int32_t* threadsFlag);
+
+#endif