[mojo] Make mojo::core::ports::NodeName and mojo::core::ports::PortName constexpr.

check_static_initializers fails because of:
---
# 0x10beb30 name.cc _GLOBAL__sub_I_name.cc
Symbol missing source lines. Showing raw disassembly (via objdump).
This might be verbose due to inlined functions.

nacl_helper:	file format elf64-x86-64

Disassembly of section .text:

00000000010beb30 <_GLOBAL__sub_I_name.cc>:
 10beb30: 55                           	pushq	%rbp
 10beb31: 48 89 e5                     	movq	%rsp, %rbp
 10beb34: 48 ff 05 ed bf 14 00         	incq	0x14bfed(%rip)          # 0x120ab28 <__profc__ZN4mojo4core5ports8PortNameC2Emm>
 10beb3b: 0f 57 c0                     	xorps	%xmm0, %xmm0
 10beb3e: 0f 11 05 2b a4 40 00         	movups	%xmm0, 0x40a42b(%rip)   # 0x14c8f70 <mojo::core::ports::kInvalidPortName>
 10beb45: 48 ff 05 e4 bf 14 00         	incq	0x14bfe4(%rip)          # 0x120ab30 <__profc__ZN4mojo4core5ports8NodeNameC2Emm>
 10beb4c: 48 83 05 44 76 0c 00 02      	addq	$0x2, 0xc7644(%rip)     # 0x1186198 <__profc__ZN4mojo4core5ports4NameC2Emm>
 10beb54: 0f 11 05 25 a4 40 00         	movups	%xmm0, 0x40a425(%rip)   # 0x14c8f80 <mojo::core::ports::kInvalidNodeName>
 10beb5b: 5d                           	popq	%rbp
 10beb5c: c3                           	retq
---
Sample build failure: https://ci.chromium.org/ui/p/chromium/builders/try/linux-rel-cft/9/overview

Change-Id: I03bbd94c6bbc760f29e34353d8ad00ee1eefe1d9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4083906
Reviewed-by: Alex Gough <ajgo@chromium.org>
Commit-Queue: Takashi Sakamoto <tasak@google.com>
Cr-Commit-Position: refs/heads/main@{#1080188}

mojo/core/ports/name.cc

@@ -8,9 +8,9 @@ namespace mojo {
 namespace core {
 namespace ports {
 
-const PortName kInvalidPortName = {0, 0};
+constexpr PortName kInvalidPortName = {0, 0};
 
-const NodeName kInvalidNodeName = {0, 0};
+constexpr NodeName kInvalidNodeName = {0, 0};
 
 std::ostream& operator<<(std::ostream& stream, const Name& name) {
   std::ios::fmtflags flags(stream.flags());

mojo/core/ports/name.h

@@ -18,7 +18,7 @@ namespace core {
 namespace ports {
 
 struct COMPONENT_EXPORT(MOJO_CORE_PORTS) Name {
-  Name(uint64_t v1, uint64_t v2) : v1(v1), v2(v2) {}
+  constexpr Name(uint64_t v1, uint64_t v2) : v1(v1), v2(v2) {}
   uint64_t v1, v2;
 };
 
@@ -38,15 +38,15 @@ COMPONENT_EXPORT(MOJO_CORE_PORTS)
 std::ostream& operator<<(std::ostream& stream, const Name& name);
 
 struct COMPONENT_EXPORT(MOJO_CORE_PORTS) PortName : Name {
-  PortName() : Name(0, 0) {}
-  PortName(uint64_t v1, uint64_t v2) : Name(v1, v2) {}
+  constexpr PortName() : Name(0, 0) {}
+  constexpr PortName(uint64_t v1, uint64_t v2) : Name(v1, v2) {}
 };
 
 extern COMPONENT_EXPORT(MOJO_CORE_PORTS) const PortName kInvalidPortName;
 
 struct COMPONENT_EXPORT(MOJO_CORE_PORTS) NodeName : Name {
-  NodeName() : Name(0, 0) {}
-  NodeName(uint64_t v1, uint64_t v2) : Name(v1, v2) {}
+  constexpr NodeName() : Name(0, 0) {}
+  constexpr NodeName(uint64_t v1, uint64_t v2) : Name(v1, v2) {}
 };
 
 extern COMPONENT_EXPORT(MOJO_CORE_PORTS) const NodeName kInvalidNodeName;