[analyzer] When a symbol is null, we should track its constraints.

Because of this, we would previously emit NO path notes when a parameter
is constrained to null (because there are no stores). Now we show where we
made the assumption, which is much more useful.

llvm-svn: 161280
diff --git a/clang/test/Analysis/method-call-path-notes.cpp b/clang/test/Analysis/method-call-path-notes.cpp
index 1e17b83..6298ca0 100644
--- a/clang/test/Analysis/method-call-path-notes.cpp
+++ b/clang/test/Analysis/method-call-path-notes.cpp
@@ -24,7 +24,7 @@
 }
 
 void test_ic_null(TestInstanceCall *p) {
-  if (!p) // expected-note {{Taking true branch}}
+  if (!p) // expected-note {{Assuming pointer value is null}} expected-note {{Taking true branch}}
     p->foo(); // expected-warning {{Called C++ object pointer is null}} expected-note{{Called C++ object pointer is null}}
 }