Convert tables in keycode_converter to constexpr.

Currently, it is not constexpr, so may not be built on compile time.
Actually, no-op editing of the keycode_converter.cc sometimes
triggers static initializer check.

Specifically, DomKey used in the tables is not constexpr aware,
so this CL makes the change.

BUG=1137426
TEST=Built on mac-rel bot. Made sure no static initializer check error.

Change-Id: Ib2d070c0cc29c725d4b7a0df000940685086d570
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2462978
Commit-Queue: Hidehiko Abe <hidehiko@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816557}

ui/events/keycodes/dom/dom_key.h

@@ -79,6 +79,9 @@ class DomKey {
                 "suspicious representation change");
 
  public:
+  // Following block is a technique to add inlined constant with C++14
+  // compatible way. These can be replaced with inline constexpr after
+  // C++17 support.
   enum InvalidKey : Base { NONE = 0 };
 // |dom_key_data.inc| describes the non-printable DomKey values, and is
 // included here to create constants for them in the DomKey:: scope.
@@ -91,14 +94,14 @@ class DomKey {
 #undef DOM_KEY_UNI
 
   // Create a DomKey, with the undefined-value sentinel DomKey::NONE.
-  DomKey() : value_(NONE) {}
+  constexpr DomKey() = default;
 
   // Create a DomKey from an encoded integer value. This is implicit so
   // that DomKey::NAME constants don't need to be explicitly converted
   // to DomKey.
-  DomKey(Base value) : value_(value) {
-    DCHECK(value == 0 || IsValid()) << value;
-  }
+  // After switching to C++17, this can be replaced by inline constexpr,
+  // so can be private. On runtime, FromBase is preferred.
+  constexpr DomKey(Base value) : value_(value) {}
 
   // Factory that returns a DomKey for the specified value. Returns nullopt if
   // |value| is not a valid value (or NONE).
@@ -161,7 +164,7 @@ class DomKey {
  private:
   static bool IsValidValue(Base value) { return (value & TYPE_MASK) != 0; }
 
-  Base value_;
+  Base value_ = NONE;
 };
 
 }  // namespace ui

ui/events/keycodes/dom/keycode_converter.cc

@@ -44,7 +44,7 @@ inline constexpr uint32_t CodeIfOnKeyboardPage(uint32_t usage) {
 #else
 #error Unsupported platform
 #endif
-#define DOM_CODE_DECLARATION const KeycodeMapEntry kDomCodeMappings[] =
+#define DOM_CODE_DECLARATION constexpr KeycodeMapEntry kDomCodeMappings[] =
 #include "ui/events/keycodes/dom/dom_code_data.inc"
 #undef DOM_CODE
 #undef DOM_CODE_DECLARATION
@@ -55,7 +55,7 @@ struct DomKeyMapEntry {
   const char* string;
 };
 
-#define DOM_KEY_MAP_DECLARATION const DomKeyMapEntry kDomKeyMappings[] =
+#define DOM_KEY_MAP_DECLARATION constexpr DomKeyMapEntry kDomKeyMappings[] =
 #define DOM_KEY_UNI(key, id, value) {DomKey::id, key}
 #define DOM_KEY_MAP(key, id, value) {DomKey::id, key}
 #include "ui/events/keycodes/dom/dom_key_data.inc"