Fix crash in optmization guide if no hints configured

Bug: 788900
Change-Id: Ia15c1712bc894b2c69920d37192c75b47dc67fbe
Reviewed-on: https://chromium-review.googlesource.com/794170Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Commit-Queue: Doug Arnett <dougarnett@chromium.org>
Cr-Commit-Position: refs/heads/master@{#519749}

components/previews/content/previews_optimization_guide.cc

@@ -128,6 +128,9 @@ PreviewsOptimizationGuide::~PreviewsOptimizationGuide() {
 
 bool PreviewsOptimizationGuide::IsWhitelisted(const net::URLRequest& request,
                                               PreviewsType type) const {
+  if (!hints_)
+    return false;
+
   return hints_->IsWhitelisted(request.url(), type);
 }
 

components/previews/content/previews_optimization_guide_unittest.cc

@@ -95,6 +95,12 @@ class PreviewsOptimizationGuideTest : public testing::Test {
   DISALLOW_COPY_AND_ASSIGN(PreviewsOptimizationGuideTest);
 };
 
+TEST_F(PreviewsOptimizationGuideTest, IsWhitelistedWithoutHints) {
+  std::unique_ptr<net::URLRequest> request =
+      CreateRequestWithURL(GURL("https://m.facebook.com"));
+  EXPECT_FALSE(guide()->IsWhitelisted(*request, PreviewsType::NOSCRIPT));
+}
+
 TEST_F(PreviewsOptimizationGuideTest,
        ProcessHintsWhitelistForNoScriptPopulatedCorrectly) {
   optimization_guide::proto::Configuration config;