Replace magic number in SafeBrowsingFeatures test.

Currently SafeBrowsingFeatures test checks extracted safe browsing
threat type for equality to 3, but should check for
SB_THREAT_TYPE_URL_MALWARE (Which does not equals to 3 in Yandex code).

Change-Id: Ifd8e554201c8467e7836f1ebd11589bff06ff2a8
Reviewed-on: https://chromium-review.googlesource.com/979792Reviewed-by: Jialiu Lin <jialiul@chromium.org>
Commit-Queue: Kalugin Alexander <akalugin@yandex-team.ru>
Cr-Commit-Position: refs/heads/master@{#546004}

chrome/browser/safe_browsing/browser_feature_extractor_unittest.cc

@@ -602,7 +602,8 @@ TEST_F(BrowserFeatureExtractorTest, SafeBrowsingFeatures) {
        features::kSafeBrowsingOriginalUrl,
         "http://www.good.com/")));
   EXPECT_DOUBLE_EQ(1.0, features[features::kSafeBrowsingIsSubresource]);
-  EXPECT_DOUBLE_EQ(3.0, features[features::kSafeBrowsingThreatType]);
+  EXPECT_DOUBLE_EQ(SB_THREAT_TYPE_URL_MALWARE,
+                   features[features::kSafeBrowsingThreatType]);
 }
 
 TEST_F(BrowserFeatureExtractorTest, MalwareFeatures) {