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..dcbbf6cd8dbd964c5c788aa95304919ed06ee976 100644
--- a/ipc/ipc_message_utils.h
+++ b/ipc/ipc_message_utils.h
@@ -307,6 +307,46 @@ 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]> {
+  using param_type = P[Size];
+  static void GetSize(base::PickleSizer* sizer, const param_type& p) {
+    GetParamSize(sizer, base::checked_cast<int>(Size));

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

Switched to checked_cast per your comment.

[Tom Sepez, 2017/02/09 17:14:37]

Why are we passing the size over the wire?  These templates apply to arrays of
known size, and we should just read/write the expected number of members.

[ericrk, 2017/02/09 22:02:08]

True enough, I guess I was thinking it was more robust against malformed data,
but it does seem pretty unlikely that this would help us. Removed.

+    for (size_t i = 0; i < Size; i++)
+      GetParamSize(sizer, p[i]);
+  }
+  static void Write(base::Pickle* m, const param_type& p) {
+    WriteParam(m, base::checked_cast<int>(Size));
+    for (size_t i = 0; i < Size; i++)

[Tom Sepez, 2017/02/09 17:17:10]

nit: can we use a range-based for loop and avoid having an index variable at
all?

[ericrk, 2017/02/09 22:02:08]

Yup, we can.

+      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 mismatch indicates invalid data.
+    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) {
+    l->append("[");
+    for (size_t i = 0; i < Size; ++i) {
+      if (i != 0)
+        l->append(" ");
+      LogParam((p[i]), l);
+    }
+    l->append("]");
+  }
+};
+
 // STL ParamTraits -------------------------------------------------------------
 
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