[mojo] Use base::Pickle for Message storage.

base/pickle.h

Index: base/pickle.h
diff --git a/base/pickle.h b/base/pickle.h
index 72b33ddc979a50a3f8fc0ecbd628889212f99a78..5a77ed7404591d8307ba952cde096a0122ea0a50 100644
--- a/base/pickle.h
+++ b/base/pickle.h
@@ -258,6 +258,18 @@ class BASE_EXPORT Pickle {
   // of the header.
   void Resize(size_t new_capacity);
 
+  // Claims |num_bytes| bytes of payload. This is similar to Reserve in that it

[yzshen1, 2015/12/15 19:07:02]

style nit: Reserve -> Reserve() and |ClaimBytes| -> ClaimBytes().
I think that is more commonly used and consistent with line 210.

(And I think I saw some other places in this CL, too.)

+  // may grow the capacity, but it also advances the write offset of the pickle
+  // by |num_bytes|. Claimed memory is NOT initialized, though any alignment
+  // padding is zeroed.
+  //
+  // Unless you're SURE you're going to write to all the allocated bytes, you
+  // should use |ClaimBytes| instead.
+  void* ClaimUninitializedBytes(size_t num_bytes);
+
+  // Claims |num_bytes| bytes of payload, zeroing its contents.
+  void* ClaimBytes(size_t num_bytes);
+
   // Find the end of the pickled data that starts at range_start.  Returns NULL
   // if the entire Pickle is not found in the given data range.
   static const char* FindNext(size_t header_size,
@@ -299,6 +311,8 @@ class BASE_EXPORT Pickle {
     WriteBytesStatic<sizeof(data)>(&data);
     return true;
   }
+
+  inline void* ClaimUninitializedBytesInternal(size_t num_bytes);
   inline void WriteBytesCommon(const void* data, size_t length);
 
   FRIEND_TEST_ALL_PREFIXES(PickleTest, DeepCopyResize);