Fix HistogramTester::GetAllSamples when empty.

Fix GetAllSamples to return an empty vector when the histogram has no
samples, instead of crashing.

BUG=

Review URL: https://codereview.chromium.org/1265403003

Cr-Commit-Position: refs/heads/master@{#342634}

2 files changed, 13 insertions, 5 deletions

diff --git a/base/test/histogram_tester.cc b/base/test/histogram_tester.cc
index 051f599..09b4ef3 100644
--- a/base/test/histogram_tester.cc
+++ b/base/test/histogram_tester.cc
@@ -79,11 +79,13 @@ std::vector<Bucket> HistogramTester::GetAllSamples(
   std::vector<Bucket> samples;
   scoped_ptr<HistogramSamples> snapshot =
       GetHistogramSamplesSinceCreation(name);
-  for (auto it = snapshot->Iterator(); !it->Done(); it->Next()) {
-    HistogramBase::Sample sample;
-    HistogramBase::Count count;
-    it->Get(&sample, nullptr, &count);
-    samples.push_back(Bucket(sample, count));
+  if (snapshot) {
+    for (auto it = snapshot->Iterator(); !it->Done(); it->Next()) {
+      HistogramBase::Sample sample;
+      HistogramBase::Count count;
+      it->Get(&sample, nullptr, &count);
+      samples.push_back(Bucket(sample, count));
+    }
   }
   return samples;
 }
diff --git a/base/test/histogram_tester_unittest.cc b/base/test/histogram_tester_unittest.cc
index d4812d7..21b8170 100644
--- a/base/test/histogram_tester_unittest.cc
+++ b/base/test/histogram_tester_unittest.cc
@@ -11,6 +11,7 @@
 #include "testing/gtest/include/gtest/gtest.h"
 
 using ::testing::ElementsAre;
+using ::testing::IsEmpty;
 
 namespace {
 
@@ -110,4 +111,9 @@ 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