Pre-allocate more string buffers in barcode code

Another couple of examples where the slow down in the barcode code
can be fixed by reserving and thus pre-allocating the buffer that
backs the Widestring. Doing += in a tight loop caused reallocation
thrashing.

BUG=chromium:834630

Change-Id: I48a802225351bcaf992c324732fddf81639b4898
Reviewed-on: https://pdfium-review.googlesource.com/31230
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Henrique Nakashima <hnakashima@chromium.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/fxbarcode/datamatrix/BC_Base256Encoder.cpp b/fxbarcode/datamatrix/BC_Base256Encoder.cpp
index b7dd69c0f7..1010cfe32c 100644
--- a/fxbarcode/datamatrix/BC_Base256Encoder.cpp
+++ b/fxbarcode/datamatrix/BC_Base256Encoder.cpp
@@ -35,6 +35,7 @@ int32_t CBC_Base256Encoder::getEncodingMode() {
 }
 void CBC_Base256Encoder::Encode(CBC_EncoderContext& context, int32_t& e) {
   WideString buffer;
+  buffer.Reserve(context.getRemainingCharacters() + 1);
   buffer += L'\0';
   while (context.hasMoreCharacters()) {
     wchar_t c = context.getCurrentChar();