Fix broken coverage_report.py

It appears that some of my final changes to coverage_report.py didn't
make it into the patch that I submitted. This means that the current
version of the script in the repo does not work.

Bug:
Change-Id: I8822840f8e3d9b6f75224bb811209860c8191026
Reviewed-on: https://pdfium-review.googlesource.com/9511
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
diff --git a/tools/coverage/coverage_report.py b/tools/coverage/coverage_report.py
index 9d6a95c..c74b6bf 100755
--- a/tools/coverage/coverage_report.py
+++ b/tools/coverage/coverage_report.py
@@ -22,7 +22,7 @@
 # 'binary' is the file that is to be run for the test.
 # 'use_test_runner' indicates if 'binary' depends on test_runner.py and thus
 # requires special handling.
-TestSpec = namedtuple('binary', 'use_test_runner')
+TestSpec = namedtuple('TestSpec', 'binary, use_test_runner')
 
 # All of the coverage tests that the script knows how to run.
 COVERAGE_TESTS = {
@@ -150,12 +150,12 @@
                                            'tools')
     coverage_tests = {}
     for name in COVERAGE_TESTS.keys():
-      (binary, uses_test_runner) = COVERAGE_TESTS[name]
-      if uses_test_runner:
-        binary_path = os.path.join(testing_tools_directory, binary)
+      test_spec = COVERAGE_TESTS[name]
+      if test_spec.use_test_runner:
+        binary_path = os.path.join(testing_tools_directory, test_spec.binary)
       else:
-        binary_path = os.path.join(self.build_directory, binary)
-      coverage_tests[name] = (binary_path, uses_test_runner)
+        binary_path = os.path.join(self.build_directory, test_spec.binary)
+      coverage_tests[name] = TestSpec(binary_path, test_spec.use_test_runner)
 
     if args['tests']:
       return {name: spec