Adding build-time option to enable the tracing of skia events in

skia/config/SkUserConfig.h

Index: skia/config/SkUserConfig.h
===================================================================
--- skia/config/SkUserConfig.h	(revision 129170)
+++ skia/config/SkUserConfig.h	(working copy)
@@ -156,6 +156,18 @@
 #define SK_SUPPORT_UNITTEST
 #endif
 
+/* If your system embeds skia and has complex event logging, define this
+   symbol to name a file that maps the following macros to your system's
+   equivalents:
+       SK_TRACE_EVENT0(event)
+       SK_TRACE_EVENT1(event, name1, value1)
+       SK_TRACE_EVENT2(event, name1, value1, name2, value2)
+   src/utils/SkDebugTrace.h has a trivial implementation that writes to
+   the debug output stream. If SK_USER_TRACE_INCLUDE_FILE is not defined,
+   SkTrace.h will define the above three macros to do nothing.
+*/
+#undef SK_USER_TRACE_INCLUDE_FILE
+
 /* If this is not defined, skia dithers gradients. Turning this on will make
    gradients look better, but might have a performance impact. When it's turned
    on, several webkit pixel tests will need to be rebaselined, too.