initial import of Chrome's trace_event into skia framework

This patch includes a modified version of Chrome's trace_event.h, which provides
tracing macros that can easily integrate into the about://tracing framework.

Currently the macros link to a default implementation of the (narrow) tracing
class SkDefaultEventTracer which does nothing; next step will be to have Chrome
subclass the SkEventTracer with a shim that bolts Skia's trace events to its own,
allowing Skia's trace events to show up in about://tracing.

I've verified that this file builds properly, and when I added a simple scoped
TRACE_EVENT0 to SkCanvas::drawRect, along with some debug prints in the NOP
implementation of tracing, I saw what I expected printed to the screen.

BUG=skia:
R=nduca@chromium.org, reed@google.com, mtklein@google.com, bsalomon@google.com

Author: humper@google.com

Review URL: https://codereview.chromium.org/149563004

git-svn-id: http://skia.googlecode.com/svn/trunk@13256 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gyp/utils.gyp b/gyp/utils.gyp
index e9e9109..3f6e5b5 100644
--- a/gyp/utils.gyp
+++ b/gyp/utils.gyp
@@ -41,6 +41,7 @@
         '../include/utils/SkDebugUtils.h',
         '../include/utils/SkDeferredCanvas.h',
         '../include/utils/SkDumpCanvas.h',
+        '../include/utils/SkEventTracer.h',
         '../include/utils/SkInterpolator.h',
         '../include/utils/SkLayer.h',
         '../include/utils/SkMatrix44.h',
@@ -74,6 +75,7 @@
         '../src/utils/SkCullPoints.cpp',
         '../src/utils/SkDeferredCanvas.cpp',
         '../src/utils/SkDumpCanvas.cpp',
+        '../src/utils/SkEventTracer.cpp',
         '../src/utils/SkFloatUtils.h',
         '../src/utils/SkGatherPixelRefsAndRects.cpp',
         '../src/utils/SkGatherPixelRefsAndRects.h',