Expose global state variables for sampling tracing to WebKit

webkit/glue/webkitplatformsupport_impl.cc

Index: webkit/glue/webkitplatformsupport_impl.cc
diff --git a/webkit/glue/webkitplatformsupport_impl.cc b/webkit/glue/webkitplatformsupport_impl.cc
index e63d76230ab80dcbd8198e0540da630f20562a68..43f3a62be8bee292589038a338ea1da9afc7518b 100644
--- a/webkit/glue/webkitplatformsupport_impl.cc
+++ b/webkit/glue/webkitplatformsupport_impl.cc
@@ -10,7 +10,6 @@
 
 #include "base/allocator/allocator_extension.h"
 #include "base/bind.h"
-#include "base/debug/trace_event.h"
 #include "base/memory/discardable_memory.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/singleton.h"
@@ -453,6 +452,24 @@ const unsigned char* WebKitPlatformSupportImpl::getTraceCategoryEnabledFlag(
   return TRACE_EVENT_API_GET_CATEGORY_ENABLED(category_name);
 }
 
+TRACE_EVENT_API_ATOMIC_WORD* WebKitPlatformSupportImpl::getTraceSamplingState(
+    const unsigned thread_bucket) {
+  switch(thread_bucket) {

[abarth-chromium, 2013/02/27 02:58:00]

Is this really better than a branch +
TRACE_EVENT_API_THREAD_BUCKET(thread_bucket)

[haraken, 2013/02/27 03:29:55]

I cannot use it because it results in 'g_trace_statethread_bucket', not
'g_trace_state0'...

(This method is called only three times at the initialization step, so the
performance wouldn't be a problem.)

+  case 0:
+    return reinterpret_cast<TRACE_EVENT_API_ATOMIC_WORD*>(
+        &TRACE_EVENT_API_THREAD_BUCKET(0));
+  case 1:
+    return reinterpret_cast<TRACE_EVENT_API_ATOMIC_WORD*>(
+        &TRACE_EVENT_API_THREAD_BUCKET(1));
+  case 2:
+    return reinterpret_cast<TRACE_EVENT_API_ATOMIC_WORD*>(
+        &TRACE_EVENT_API_THREAD_BUCKET(2));
+  default:
+    NOTREACHED() << "Unknown thread bucket type.";
+  }
+  return NULL;
+}
+
 void WebKitPlatformSupportImpl::addTraceEvent(
     char phase,
     const unsigned char* category_enabled,