Add dictionary to css_parser_proto_fuzzer

TBR=meade@chromium.org

Bug: 771641
Change-Id: Ibeebf55dfb82c48d32b85a5b97209b1567641b10
Reviewed-on: https://chromium-review.googlesource.com/744311
Commit-Queue: Jonathan Metzman <metzman@chromium.org>
Reviewed-by: Max Moroz <mmoroz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513055}

third_party/WebKit/Source/core/BUILD.gn

@@ -1847,6 +1847,7 @@ if (!is_win) {
       "//third_party/WebKit/Source/platform:blink_fuzzer_test_support",
       "//third_party/libprotobuf-mutator",
     ]
+    dict = "//third_party/WebKit/Source/core/css/css.dict"
   }
 
   proto_library("css_proto") {