Add IPC ParamTraits for c-style arrays

ipc/ipc_message_utils.h

Index: ipc/ipc_message_utils.h
diff --git a/ipc/ipc_message_utils.h b/ipc/ipc_message_utils.h
index 58d6aa26da34fb125d45bd9f2ddd3f767a2f7313..1da8a65ad4b6e3275e347ca11d29c403b7ed344c 100644
--- a/ipc/ipc_message_utils.h
+++ b/ipc/ipc_message_utils.h
@@ -307,6 +307,47 @@ struct IPC_EXPORT ParamTraits<double> {
   static void Log(const param_type& p, std::string* l);
 };
 
+template <class P, size_t Size>
+struct ParamTraits<P[Size]> {
+  static_assert(
+      Size <= std::numeric_limits<int>::max(),
+      "ParamTraits for fixed-size arrays only supports sizes under max int.");
+  using param_type = P[Size];
+  static void GetSize(base::PickleSizer* sizer, const param_type& p) {
+    GetParamSize(sizer, static_cast<int>(Size));
+    for (size_t i = 0; i < Size; i++)
+      GetParamSize(sizer, p[i]);
+  }
+  static void Write(base::Pickle* m, const param_type& p) {
+    WriteParam(m, static_cast<int>(Size));
+    for (size_t i = 0; i < Size; i++)
+      WriteParam(m, p[i]);
+  }
+  static bool Read(const base::Pickle* m,
+                   base::PickleIterator* iter,
+                   param_type* r) {
+    int size;
+    // ReadLength() checks for < 0 itself.
+    if (!iter->ReadLength(&size))
+      return false;
+    // For a fixed size array, a size mismath indicates invalid data.

[dcheng, 2017/02/08 19:21:11]

Nit: mismatch

[ericrk, 2017/02/08 21:07:15]

Done.

+    if (size != Size)
+      return false;
+    for (size_t i = 0; i < Size; i++) {
+      if (!ReadParam(m, iter, &(*r)[i]))
+        return false;
+    }
+    return true;
+  }
+  static void Log(const param_type& p, std::string* l) {
+    for (size_t i = 0; i < Size; ++i) {

[vmpstr, 2017/02/08 20:06:11]

drive-by: In the other files where we do something in the log, we also append [
and ] to the start and end respectively, so that it kind of looks like an array,
I guess. Should we do the same thing here?

[ericrk, 2017/02/08 21:07:15]

This is pretty inconsistent - CC already has traits for a number of vectors,
which don't have "[", "]", it did use brackets on its arrays though... I guess
the brackets probably look better. Added.

+      if (i != 0)
+        l->append(" ");
+      LogParam((p[i]), l);
+    }
+  }
+};
+
 // STL ParamTraits -------------------------------------------------------------
 
 template <>