Remove trailing whitespace.

Also adds a presubmit to prevent adding trailing whitespace to source
code in the future.

Change-Id: I41a4df81487f6f00aa19b188f0cac6a3377efde6
Reviewed-on: https://skia-review.googlesource.com/57380
Reviewed-by: Ravi Mistry <rmistry@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 0fe4841..0f37de4 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -225,6 +225,9 @@
   results.extend(
       input_api.canned_checks.CheckChangeHasNoCR(
           input_api, output_api, source_file_filter=sources))
+  results.extend(
+      input_api.canned_checks.CheckChangeHasNoStrayWhitespace(
+          input_api, output_api, source_file_filter=sources))
   results.extend(_PythonChecks(input_api, output_api))
   results.extend(_IfDefChecks(input_api, output_api))
   results.extend(_CopyrightChecks(input_api, output_api,