i18n: Fix a crash because of unaligned memory accesses.

The buffer used in placement new should have the same alignment
as the underlying type DecimalFormatProperties.
Fixes login crashes in Chrome OS.

BUG=chromium:865100
TEST=locally built chrome os image works.

Change-Id: Ic71cb4e7962f1b9170e0a4ef00223767c621bc67
Reviewed-on: https://chromium-review.googlesource.com/1145582
Reviewed-by: Jungshik Shin <jshin@chromium.org>

Author: m-gupta

README.chromium

@@ -260,3 +260,8 @@ D. Local Modifications
   - upstream bug:
     https://unicode-org.atlassian.net/browse/ICU-13852
 
+11. Align memory buffer used in Decimal Format
+
+  - patches/decimalformat_align.patch
+  - upstream bug:
+    https://unicode-org.atlassian.net/browse/ICU-20039

patches/decimalformat_align.patch

@@ -0,0 +1,13 @@
+diff --git a/source/i18n/number_decimfmtprops.cpp b/source/i18n/number_decimfmtprops.cpp
+index 6754fe19..b8994e56 100644
+--- a/source/i18n/number_decimfmtprops.cpp
++++ b/source/i18n/number_decimfmtprops.cpp
+@@ -15,7 +15,7 @@ using namespace icu::number::impl;
+ 
+ namespace {
+ 
+-char kRawDefaultProperties[sizeof(DecimalFormatProperties)];
++alignas(DecimalFormatProperties) char kRawDefaultProperties[sizeof(DecimalFormatProperties)];
+ 
+ icu::UInitOnce gDefaultPropertiesInitOnce = U_INITONCE_INITIALIZER;
+ 

source/i18n/number_decimfmtprops.cpp

@@ -15,7 +15,7 @@ using namespace icu::number::impl;
 
 namespace {
 
-char kRawDefaultProperties[sizeof(DecimalFormatProperties)];
+alignas(DecimalFormatProperties) char kRawDefaultProperties[sizeof(DecimalFormatProperties)];
 
 icu::UInitOnce gDefaultPropertiesInitOnce = U_INITONCE_INITIALIZER;