Merge to XFA: Use _GLIBCXX_DEBUG in standalone Debug builds on Linux.

TBR=ochang@chromium.org

Review URL: https://codereview.chromium.org/1588643003 .

(cherry picked from commit 783709f76baf7893b7334209fe89d947acd6369d)

Review URL: https://codereview.chromium.org/1584713004 .
diff --git a/build/standalone.gypi b/build/standalone.gypi
index 536c255..72975bc 100644
--- a/build/standalone.gypi
+++ b/build/standalone.gypi
@@ -100,6 +100,12 @@
         'xcode_settings': {
           'GCC_OPTIMIZATION_LEVEL': '0',  # -O0
         },
+        'conditions': [
+          ['OS=="linux"', {
+            # Enable libstdc++ debugging to help catch problems early.
+            'defines': ['_GLIBCXX_DEBUG=1',],
+          }],
+        ],
       },
       'Release': {
         'cflags': [