Add skia_tsan_build to match skia_asan_build and fix one example race.

R=mtklein@google.com

Review URL: https://codereview.chromium.org/24644003

git-svn-id: http://skia.googlecode.com/svn/trunk@11464 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gyp/common_conditions.gypi b/gyp/common_conditions.gypi
index f9feb1c..f8012b9 100644
--- a/gyp/common_conditions.gypi
+++ b/gyp/common_conditions.gypi
@@ -286,6 +286,15 @@
               '-fsanitize=address',
             ],
           }],
+          [ 'skia_tsan_build', {
+            'cflags': [
+              '-fsanitize=thread',
+              '-fno-omit-frame-pointer',
+            ],
+            'ldflags': [
+              '-fsanitize=thread',
+            ],
+          }],
           [ 'skia_clang_build', {
             'cflags': [
               '-Wstring-conversion',