Fix missing comma in core.gypi

BUG=
TBR=brucedawson, eae, leviw

Review URL: https://codereview.chromium.org/1305943004

git-svn-id: svn://svn.chromium.org/blink/trunk@201148 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/core.gypi

@@ -1136,7 +1136,7 @@
             'css/FontSize.cpp',
             'css/FontSize.h',
             'css/FontStyleMatcher.cpp',
-            'css/FontStyleMatcher.h'
+            'css/FontStyleMatcher.h',
             'css/HashTools.h',
             'css/KeyframeStyleRuleCSSStyleDeclaration.cpp',
             'css/KeyframeStyleRuleCSSStyleDeclaration.h',