2 files changed, 35 insertions, 2 deletions
diff --git a/extensions/browser/file_highlighter.cc b/extensions/browser/file_highlighter.cc
index d3edeca..2cc669e 100644
--- a/extensions/browser/file_highlighter.cc
+++ b/extensions/browser/file_highlighter.cc
@@ -203,8 +203,19 @@ SourceHighlighter::~SourceHighlighter() {
 }
 
 void SourceHighlighter::Parse(size_t line_number) {
-  for (size_t i = 1; i < line_number; ++i)
-    start_ = contents_.find('\n', start_) + 1;
+  // If line 0 is requested, highlight nothing.
+  if (line_number == 0) {
+    start_ = contents_.size();
+    return;
+  }
+
+  for (size_t i = 1; i < line_number; ++i) {
+    start_ = contents_.find('\n', start_);
+    if (start_ == std::string::npos)
+      break;
+    start_ += 1;
+  }
+
   end_ = contents_.find('\n', start_);
 
   // If we went off the end of the string (i.e., the line number was invalid),
diff --git a/extensions/browser/file_highlighter_unittest.cc b/extensions/browser/file_highlighter_unittest.cc
index 6352be4..a449bf9 100644
--- a/extensions/browser/file_highlighter_unittest.cc
+++ b/extensions/browser/file_highlighter_unittest.cc
@@ -95,4 +95,26 @@ TEST(ManifestHighlighterUnitTest, ManifestHighlighterUnitTest) {
   EXPECT_EQ(kInternationalFeature, international_feature.GetFeature());
 }
 
+TEST(SouceHighlighterUnitTest, SourceHighlighterUnitTest) {
+  const char kBasicSourceFile[] = "line one\nline two\nline three";
+
+  SourceHighlighter basic1(kBasicSourceFile, 1u);
+  EXPECT_EQ("line one", basic1.GetFeature());
+  SourceHighlighter basic2(kBasicSourceFile, 2u);
+  EXPECT_EQ("line two", basic2.GetFeature());
+  SourceHighlighter basic3(kBasicSourceFile, 3u);
+  EXPECT_EQ("line three", basic3.GetFeature());
+
+  const char kNoNewlineSourceFile[] = "thisisonelonglinewithnobreaksinit";
+
+  SourceHighlighter full_line(kNoNewlineSourceFile, 1u);
+  EXPECT_EQ(kNoNewlineSourceFile, full_line.GetFeature());
+
+  SourceHighlighter line_zero(kNoNewlineSourceFile, 0u);
+  EXPECT_EQ(EmptyString(), line_zero.GetFeature());
+
+  SourceHighlighter out_of_bounds(kNoNewlineSourceFile, 2u);
+  EXPECT_EQ(EmptyString(), out_of_bounds.GetFeature());
+}
+
 }  // namespace extensions