Document LEAK_SANITIZER_IGNORE_OBJECT() more precisely.

third_party/WebKit/Source/wtf/LeakAnnotations.h

Index: third_party/WebKit/Source/wtf/LeakAnnotations.h
diff --git a/third_party/WebKit/Source/wtf/LeakAnnotations.h b/third_party/WebKit/Source/wtf/LeakAnnotations.h
index 446992db6abf6cfefb9bc9473bcd08dc45da6daf..6ce298fbdd404ebdb1b3c7217b9638dcd17c8530 100644
--- a/third_party/WebKit/Source/wtf/LeakAnnotations.h
+++ b/third_party/WebKit/Source/wtf/LeakAnnotations.h
@@ -34,11 +34,7 @@
 
 // This file defines macros for working with LeakSanitizer, allowing memory
 // and allocations to be registered as exempted from LSan consideration.
-//
-// LSan exempted memory will be treated as a source of live pointers,
-// i.e. heap objects reachable by following pointers from an exempted
-// object will not be reported as leaks.
-//
+
 #include "wtf/Noncopyable.h"
 #if USE(LEAK_SANITIZER)
 #include "wtf/AddressSanitizer.h"
@@ -74,6 +70,15 @@ public:
 
 // LEAK_SANITIZER_IGNORE_OBJECT(X): the heap object referenced by pointer X
 // will be ignored by LSan.
+//
+// "Ignorance" means that LSan's leak detection pass will not consider the
+// ignored memory chunk as leaking. Furthermore, the LSan reachability
+// pass will not scan an ignored memory chunk for live, reachable pointers.
+// So, should any of the pointers of that ignored chunk not be reachable
+// from elsewhere, they'll be unreachable and thus not be reported as leaking.
+//
+// Notice that LSan will not transitively compute what's reachable from an
+// ignored memory chunk and consider that set as ignored and unreachable.

[haraken, 2015/12/11 09:46:36]

Slightly better: lsan_ignore_object(X) means that LSan ignores the object graph
starting with X. It does not mean that LSan considers the objects reachable from
X are unreachable.

[sof, 2015/12/11 10:03:37]

A bit too brief perhaps? It ignores the object at X, not its object graph.

 #define LEAK_SANITIZER_IGNORE_OBJECT(X) __lsan_ignore_object(X)
 
 // If the object pointed to by the static local is on the Oilpan heap, a strong