Fix HistogramTester::GetAllSamples when empty.

base/test/histogram_tester_unittest.cc

Index: base/test/histogram_tester_unittest.cc
diff --git a/base/test/histogram_tester_unittest.cc b/base/test/histogram_tester_unittest.cc
index 8452013f036c7b125deb9076d0864ca111c0409b..71d68884934e03c0a81ee41a580b65109af000f1 100644
--- a/base/test/histogram_tester_unittest.cc
+++ b/base/test/histogram_tester_unittest.cc
@@ -13,6 +13,7 @@
 namespace base {
 
 using ::testing::ElementsAre;
+using ::testing::IsEmpty;
 
 static const char kHistogram1[] = "Test1";
 static const char kHistogram2[] = "Test2";
@@ -106,4 +107,9 @@ TEST_F(HistogramTesterTest, TestGetAllSamples) {
               ElementsAre(Bucket(2, 1), Bucket(3, 2), Bucket(5, 1)));
 }
 
+TEST_F(HistogramTesterTest, TestGetAllSamples_NoSamples) {
+  HistogramTester tester;
+  EXPECT_THAT(tester.GetAllSamples(kHistogram5), IsEmpty());
+}
+
 }  // namespace base