Bump iossim default device to 'iPhone 5s'.

iOS builds now default to 64-bit (codereview.chromium.org/1021513002). Bump
default device to iPhone 5s, which supports 64-bit binaries.

BUG=None
TEST=iossim works without passing any device flags.

Review URL: https://codereview.chromium.org/1070753004

Cr-Commit-Position: refs/heads/master@{#324283}

testing/iossim/iossim.mm

@@ -850,7 +850,8 @@ int main(int argc, char* const argv[]) {
   NSString* appPath = nil;
   NSString* appName = nil;
   NSString* sdkVersion = nil;
-  NSString* deviceName = IsRunningWithXcode6OrLater() ? @"iPhone 5" : @"iPhone";
+  NSString* deviceName =
+      IsRunningWithXcode6OrLater() ? @"iPhone 5s" : @"iPhone";
   NSString* simHomePath = nil;
   NSMutableArray* appArgs = [NSMutableArray array];
   NSMutableDictionary* appEnv = [NSMutableDictionary dictionary];