Cherry pick an upstream cl for host tz detection

source/i18n/timezone.cpp

Index: source/i18n/timezone.cpp
diff --git a/source/i18n/timezone.cpp b/source/i18n/timezone.cpp
index 6ed008df6142ca18ef5d6a14c0d95e4d333e494b..6b3f8d28ba434a1e85cd76e72a2403eca96ee804 100644
--- a/source/i18n/timezone.cpp
+++ b/source/i18n/timezone.cpp
@@ -1,6 +1,6 @@
 /*
 *******************************************************************************
-* Copyright (C) 1997-2014, International Business Machines Corporation and
+* Copyright (C) 1997-2015, International Business Machines Corporation and
 * others. All Rights Reserved.
 *******************************************************************************
 *
@@ -440,21 +440,9 @@ TimeZone::createTimeZone(const UnicodeString& ID)
 
 // -------------------------------------
 
-/**
- * Initialize DEFAULT_ZONE from the system default time zone.  
- * Upon return, DEFAULT_ZONE will not be NULL, unless operator new()
- * returns NULL.
- */
-static void U_CALLCONV initDefault()
+TimeZone* U_EXPORT2
+TimeZone::detectHostTimeZone()
 {
-    ucln_i18n_registerCleanup(UCLN_I18N_TIMEZONE, timeZone_cleanup);
-
-    // If setDefault() has already been called we can skip getting the
-    // default zone information from the system.
-    if (DEFAULT_ZONE != NULL) {
-        return;
-    }
-    
     // We access system timezone data through TPlatformUtilities,
     // including tzset(), timezone, and tzname[].
     int32_t rawOffset = 0;
@@ -463,16 +451,6 @@ static void U_CALLCONV initDefault()
     // First, try to create a system timezone, based
     // on the string ID in tzname[0].
 
-    // NOTE:  this code is safely single threaded, being only
-    // run via umtx_initOnce().
-    //
-    // Some of the locale/timezone OS functions may not be thread safe,
-    //
-    // The operating system might actually use ICU to implement timezones.
-    // So we may have ICU calling ICU here, like on AIX.
-    // There shouldn't be a problem with this; initOnce does not hold a mutex
-    // while the init function is being run.
-
     uprv_tzset(); // Initialize tz... system data
 
     // Get the timezone ID from the host.  This function should do
@@ -484,13 +462,13 @@ static void U_CALLCONV initDefault()
     // Invert sign because UNIX semantics are backwards
     rawOffset = uprv_timezone() * -U_MILLIS_PER_SECOND;
 
-    TimeZone* default_zone = NULL;
+    TimeZone* hostZone = NULL;
 
     /* Make sure that the string is NULL terminated to prevent BoundsChecker/Purify warnings. */
     UnicodeString hostStrID(hostID, -1, US_INV);
     hostStrID.append((UChar)0);
     hostStrID.truncate(hostStrID.length()-1);
-    default_zone = createSystemTimeZone(hostStrID);
+    hostZone = createSystemTimeZone(hostStrID);
 
 #if U_PLATFORM_USES_ONLY_WIN32_API
     // hostID points to a heap-allocated location on Windows.
@@ -498,30 +476,69 @@ static void U_CALLCONV initDefault()
 #endif
 
     int32_t hostIDLen = hostStrID.length();
-    if (default_zone != NULL && rawOffset != default_zone->getRawOffset()
+    if (hostZone != NULL && rawOffset != hostZone->getRawOffset()
         && (3 <= hostIDLen && hostIDLen <= 4))
     {
         // Uh oh. This probably wasn't a good id.
         // It was probably an ambiguous abbreviation
-        delete default_zone;
-        default_zone = NULL;
+        delete hostZone;
+        hostZone = NULL;
     }
 
     // Construct a fixed standard zone with the host's ID
     // and raw offset.
-    if (default_zone == NULL) {
-        default_zone = new SimpleTimeZone(rawOffset, hostStrID);
+    if (hostZone == NULL) {
+        hostZone = new SimpleTimeZone(rawOffset, hostStrID);
     }
 
     // If we _still_ don't have a time zone, use GMT.
-    if (default_zone == NULL) {
+    //
+    // Note: This is extremely unlikely situation. If
+    // new SimpleTimeZone(...) above fails, the following
+    // code may also fail.
+    if (hostZone == NULL) {
         const TimeZone* temptz = TimeZone::getGMT();
         // If we can't use GMT, get out.
         if (temptz == NULL) {
-            return;
+            return NULL;
         }
-        default_zone = temptz->clone();
+        hostZone = temptz->clone();
+    }
+
+    return hostZone;
+}
+
+// -------------------------------------
+
+/**
+ * Initialize DEFAULT_ZONE from the system default time zone.  
+ * Upon return, DEFAULT_ZONE will not be NULL, unless operator new()
+ * returns NULL.
+ */
+static void U_CALLCONV initDefault()
+{
+    ucln_i18n_registerCleanup(UCLN_I18N_TIMEZONE, timeZone_cleanup);
+
+    // If setDefault() has already been called we can skip getting the
+    // default zone information from the system.
+    if (DEFAULT_ZONE != NULL) {
+        return;
     }
+    
+    // NOTE:  this code is safely single threaded, being only
+    // run via umtx_initOnce().
+    //
+    // Some of the locale/timezone OS functions may not be thread safe,
+    //
+    // The operating system might actually use ICU to implement timezones.
+    // So we may have ICU calling ICU here, like on AIX.
+    // There shouldn't be a problem with this; initOnce does not hold a mutex
+    // while the init function is being run.
+
+    // The code detecting the host time zone was separated from this
+    // and implemented as TimeZone::detectHostTimeZone()
+
+    TimeZone *default_zone = TimeZone::detectHostTimeZone();
 
     // The only way for DEFAULT_ZONE to be non-null at this point is if the user
     // made a thread-unsafe call to setDefault() or adoptDefault() in another