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 034cf06a78a6376534b4d2bd04a06b0e0c9fc2f7..47ca9778b6708c07a1637079b81a32302651faee 100644
--- a/base/compiler_specific.h
+++ b/base/compiler_specific.h
@@ -175,17 +175,9 @@
 // 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, 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)
+#define MSAN_UNPOISON(p, s)  __msan_unpoison(p, s)
 #else  // MEMORY_SANITIZER
-#define MSAN_UNPOISON(p, size)
-#define MSAN_CHECK_MEM_IS_INITIALIZED(p, size)
+#define MSAN_UNPOISON(p, s)
 #endif  // MEMORY_SANITIZER
 
 // Macro useful for writing cross-platform function pointers.