[date] Add ICU backend for timezone info behind a flag

src/i18n.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 // limitations under the License.
 
 #ifndef V8_I18N_H_
 #define V8_I18N_H_
 
+#include "src/base/timezone-cache.h"
 #include "src/objects.h"
 #include "unicode/uversion.h"
 
 namespace U_ICU_NAMESPACE {
 class BreakIterator;
 class Collator;
 class DecimalFormat;
 class SimpleDateFormat;
+class TimeZone;
 }
 
 namespace v8 {
 namespace internal {
 
 template <typename T>
 class Handle;
 
 class DateFormat {
  public:
@@ skipping 94 matching lines @@
 
   // Layout description.
   static const int kBreakIterator = JSObject::kHeaderSize;
   static const int kUnicodeString = kBreakIterator + kPointerSize;
   static const int kSize = kUnicodeString + kPointerSize;
 
  private:
   V8BreakIterator();
 };
 
+// ICUTimezoneCache calls out to ICU for TimezoneCache
+// functionality in a straightforward way.
+class ICUTimezoneCache : public base::TimezoneCache {
+ public:
+  ICUTimezoneCache();
+
+  ~ICUTimezoneCache() override;
+
+  const char* LocalTimezone(double time_ms) override;
+
+  double DaylightSavingsOffset(double time_ms) override;
+
+  double LocalTimeOffset() override;
+
+  void Clear() override;
+
+ private:
+  icu::TimeZone* GetTimeZone();
+
+  bool GetOffsets(double time_ms, int32_t* raw_offset, int32_t* dst_offset);
+
+  icu::TimeZone* timezone_;
+
+  static const int32_t kMaxTimezoneChars = 20;

[ulan, 2017/03/03 13:20:27]

Can we use std::string here?

[Dan Ehrenberg, 2017/03/03 15:06:54]

Do you mean that we'd make LocalTimezone() return an std::string, or store the
timezone locally as a string? The first seems like a reasonable idea; for the
second, I don't know how we'd do the memory management.

[ulan, 2017/03/10 17:55:38]

Ah, sorry, nevermind. I meant the second, but I see the problem now.

+  char timezone_name_[kMaxTimezoneChars];
+  char dst_timezone_name_[kMaxTimezoneChars];
+};
+
+// ICUOSTimezoneCache defers to the OS TimezoneCache
+// for LocalTimezone if ICU provides a timezone name
+// which starts with GMT. Otherwise, it uses ICU for
+// all operaitons. The issue here is that CLDR declines
+// to specify short names for many time zones, when the
+// OS often does know an appropriate short name.
+class ICUOSTimezoneCache : public ICUTimezoneCache {
+ public:
+  ICUOSTimezoneCache();
+
+  ~ICUOSTimezoneCache() override;
+
+  const char* LocalTimezone(double time_ms) override;
+
+  void Clear() override;
+
+ private:
+  TimezoneCache* os_tz_cache_;
+};
+
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_I18N_H_