Refactor PPB_Flash GetLocalTimeZoneOffset to the new PPAPI resource model

ppapi/proxy/flash_resource.cc

Index: ppapi/proxy/flash_resource.cc
diff --git a/ppapi/proxy/flash_resource.cc b/ppapi/proxy/flash_resource.cc
index be5acd3a851eb26532aa54b95d96768e90bea998..176bd168185e6705059397650a7a411e8233c207 100644
--- a/ppapi/proxy/flash_resource.cc
+++ b/ppapi/proxy/flash_resource.cc
@@ -4,15 +4,42 @@
 
 #include "ppapi/proxy/flash_resource.h"
 
+#include <cmath>
+
+#include "base/containers/mru_cache.h"
+#include "base/lazy_instance.h"
+#include "base/time.h"
 #include "ppapi/c/pp_errors.h"
 #include "ppapi/c/private/ppb_flash.h"
 #include "ppapi/proxy/plugin_globals.h"
 #include "ppapi/proxy/ppapi_messages.h"
+#include "ppapi/shared_impl/time_conversion.h"
 #include "ppapi/shared_impl/var.h"
 
 namespace ppapi {
 namespace proxy {
 
+namespace {
+
+struct LocalTimeZoneOffsetEntry {
+  base::TimeTicks expiration;
+  double offset;
+};
+
+class LocalTimeZoneOffsetCache
+    : public base::MRUCache<PP_Time, LocalTimeZoneOffsetEntry> {
+ public:
+  LocalTimeZoneOffsetCache()
+      : base::MRUCache<PP_Time, LocalTimeZoneOffsetEntry>(kCacheSize) {}
+ private:
+  static const size_t kCacheSize = 100;
+};
+
+base::LazyInstance<LocalTimeZoneOffsetCache>::Leaky
+    g_local_time_zone_offset_cache = LAZY_INSTANCE_INITIALIZER;
+
+} //  namespace
+
 FlashResource::FlashResource(Connection connection, PP_Instance instance)
     : PluginResource(connection, instance) {
   SendCreate(RENDERER, PpapiHostMsg_Flash_Create());
@@ -56,5 +83,50 @@ PP_Bool FlashResource::SetCrashData(PP_Instance instance,
   return PP_FALSE;
 }
 
+double FlashResource::GetLocalTimeZoneOffset(PP_Instance instance,
+                                             PP_Time t) {
+  LocalTimeZoneOffsetCache& cache = g_local_time_zone_offset_cache.Get();
+
+  // Get the minimum PP_Time value that shares the same minute as |t|.
+  // Use cached offset if cache hasn't expired and |t| is in the same minute as
+  // the time for the cached offset (assume offsets change on minute
+  // boundaries).
+  PP_Time t_minute_base = floor(t / 60.0) * 60.0;
+  LocalTimeZoneOffsetCache::iterator iter = cache.Get(t_minute_base);
+  base::TimeTicks now = base::TimeTicks::Now();
+  if (iter != cache.end() && now < iter->second.expiration)
+    return iter->second.offset;
+
+  // Cache the local offset for ten seconds, since it's slow on XP and Linux.
+  // Note that TimeTicks does not continue counting across sleep/resume on all
+  // platforms. This may be acceptable for 10 seconds, but if in the future this
+  // is changed to one minute or more, then we should consider using base::Time.
+  const int64 kMaxCachedLocalOffsetAgeInSeconds = 10;
+  base::TimeDelta expiration_delta =
+      base::TimeDelta::FromSeconds(kMaxCachedLocalOffsetAgeInSeconds);
+
+  LocalTimeZoneOffsetEntry cache_entry;
+  cache_entry.expiration = now + expiration_delta;
+  cache_entry.offset = 0.0;
+
+  // We can't do the conversion here on Linux because the localtime calls
+  // require filesystem access prohibited by the sandbox.
+  // TODO(shess): Figure out why OSX needs the access, the sandbox warmup should
+  // handle it.  http://crbug.com/149006
+#if defined(OS_LINUX) || defined(OS_MACOSX)
+  int32_t result = SyncCall<PpapiPluginMsg_Flash_GetLocalTimeZoneOffsetReply>(
+      BROWSER,
+      PpapiHostMsg_Flash_GetLocalTimeZoneOffset(PPTimeToTime(t)),
+      &cache_entry.offset);
+  if (result != PP_OK)
+    cache_entry.offset = 0.0;
+#else
+  cache_entry.offset = PPGetLocalTimeZoneOffset(PPTimeToTime(t));
+#endif
+
+  cache.Put(t_minute_base, cache_entry);
+  return cache_entry.offset;
+}
+
 }  // namespace proxy
 }  // namespace ppapi