Update mojo typemaps for base::Time* to pass by value.

mojo/common/common_custom_types.typemap

Index: mojo/common/common_custom_types.typemap
diff --git a/mojo/common/common_custom_types.typemap b/mojo/common/common_custom_types.typemap
index 8d88109d8c1352af4e1ba676325c3070c3417a7d..ce623878b58b1bd7875b33d94f06f5e77eb560e6 100644
--- a/mojo/common/common_custom_types.typemap
+++ b/mojo/common/common_custom_types.typemap
@@ -17,7 +17,7 @@ type_mappings = [
   "mojo.common.mojom.FilePath=base::FilePath",
   "mojo.common.mojom.DictionaryValue=base::DictionaryValue",
   "mojo.common.mojom.ListValue=base::ListValue",
-  "mojo.common.mojom.Time=base::Time",
-  "mojo.common.mojom.TimeDelta=base::TimeDelta",
-  "mojo.common.mojom.TimeTicks=base::TimeTicks",
+  "mojo.common.mojom.Time=base::Time[pass_by_value]",

[yzshen1, 2016/07/08 15:42:01]

I am planning to replace "pass_by_value" with "move_only". This change conflicts
with that.

The reason is explained in:
https://docs.google.com/document/d/1dutUW6XUlbSJzsqmtmPnN-J7R8z-iEL-QJ_GR9hWK...

In short, “pass_by_value” is not transitive. You want to pass TrivialStruct by
value doesn’t necessarily mean that you want to pass std::vector<TrivialStruct>
by value. On the other hand, "move_only" is transitive. It seems simpler to use
"move_only" and apply the following rule consistently: pass primitive types and
move-only types by value; pass other types by const ref.

[dcheng, 2016/07/08 16:21:45]

It seems unfortunate that we'll actively encourage people to go against the
guidance to pass base::Time* types by value. There's some inconsistency in the
codebase today (since this is something people often miss), but here's the
breakdown today:

base::Time: 155 by value, 199 by const ref
base::TimeDelta: 505 by value, 237 by const ref
base::TimeTicks: 328 by value, 258 by const ref

What would be the harm in just s/pass_by_value/move_only in this CL? I guess it
would cause some structs encapsulating this to be treated as move-only as well?

+  "mojo.common.mojom.TimeDelta=base::TimeDelta[pass_by_value]",
+  "mojo.common.mojom.TimeTicks=base::TimeTicks[pass_by_value]",
 ]