Revert of Revert of MSan: check data is initialized when serializing with base::Pickle.

base/compiler_specific.h

Index: base/compiler_specific.h
diff --git a/base/compiler_specific.h b/base/compiler_specific.h
index 47ca9778b6708c07a1637079b81a32302651faee..034cf06a78a6376534b4d2bd04a06b0e0c9fc2f7 100644
--- a/base/compiler_specific.h
+++ b/base/compiler_specific.h
@@ -175,9 +175,17 @@
 // Mark a memory region fully initialized.
 // Use this to annotate code that deliberately reads uninitialized data, for
 // example a GC scavenging root set pointers from the stack.
-#define MSAN_UNPOISON(p, s)  __msan_unpoison(p, s)
+#define MSAN_UNPOISON(p, size)  __msan_unpoison(p, size)
+
+// Check a memory region for initializedness, as if it was being used here.
+// If any bits are uninitialized, crash with an MSan report.
+// Use this to sanitize data which MSan won't be able to track, e.g. before
+// passing data to another process via shared memory.
+#define MSAN_CHECK_MEM_IS_INITIALIZED(p, size) \
+    __msan_check_mem_is_initialized(p, size)
 #else  // MEMORY_SANITIZER
-#define MSAN_UNPOISON(p, s)
+#define MSAN_UNPOISON(p, size)
+#define MSAN_CHECK_MEM_IS_INITIALIZED(p, size)
 #endif  // MEMORY_SANITIZER
 
 // Macro useful for writing cross-platform function pointers.