Bug 330951: Asserting that string arguments str1 and str2 arguments are not NULLs in js_CompareStrings and js_EqualStrings.

Previously passing str1 and str2 set to NULL did not crash as str1 and str2 compared equals as pointers and the functions returned true without accessing *str1 or *str2. In turn it allowed for the regression from bug 311515 causing this bug to survive much longer then it should. r=brendan.

js/src/jsstr.c

@@ -2825,6 +2825,9 @@ js_CompareStrings(JSString *str1, JSString *str2)
     const jschar *s1, *s2;
     intN cmp;
 
+    JS_ASSERT(str1);
+    JS_ASSERT(str2);
+
     /* Fast case: pointer equality could be a quick win. */
     if (str1 == str2)
         return 0;
@@ -2846,6 +2849,9 @@ js_EqualStrings(JSString *str1, JSString *str2)
     size_t n;
     const jschar *s1, *s2;
 
+    JS_ASSERT(str1);
+    JS_ASSERT(str2);
+
     /* Fast case: pointer equality could be a quick win. */
     if (str1 == str2)
         return JS_TRUE;