[Android] Ignore trailing whitespace in expectation diff-patch lines

We should not care about trailing whitespace in expectation files,
since R8 doesn't either.

Change-Id: Ief57c4c260083f662ca5b791edf7504de2e40428
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2363259
Commit-Queue: Mohamed Heikal <mheikal@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799804}

build/android/gyp/util/diff_utils.py

@@ -19,7 +19,7 @@ def _SkipOmitted(line):
   a line that changes from build to build because - for instance - it contains
   version information.
   """
-  if line.endswith('# OMIT FROM EXPECTATIONS\n'):
+  if line.rstrip().endswith('# OMIT FROM EXPECTATIONS'):
     return '# THIS LINE WAS OMITTED\n'
   return line
 
@@ -27,10 +27,14 @@ def _SkipOmitted(line):
 def _GenerateDiffWithOnlyAdditons(expected_path, actual_data):
   """Generate a diff that only contains additions"""
   # Ignore blank lines when creating the diff to cut down on whitespace-only
-  # lines in the diff.
+  # lines in the diff. Also remove trailing whitespaces and add the new lines
+  # manually (ndiff expects new lines but we don't care about trailing
+  # whitespace).
   with open(expected_path) as expected:
     expected_lines = [l for l in expected.readlines() if l.strip()]
-  actual_lines = [l for l in actual_data.splitlines(True) if l.strip()]
+  actual_lines = [
+      '{}\n'.format(l.rstrip()) for l in actual_data.splitlines() if l.strip()
+  ]
 
   diff = difflib.ndiff(expected_lines, actual_lines)
   filtered_diff = (l for l in diff if l.startswith('+'))
@@ -39,9 +43,12 @@ def _GenerateDiffWithOnlyAdditons(expected_path, actual_data):
 
 def _DiffFileContents(expected_path, actual_data):
   """Check file contents for equality and return the diff or None."""
+  # Remove all trailing whitespace and add it explicitly in the end.
   with open(expected_path) as f_expected:
-    expected_lines = f_expected.readlines()
-  actual_lines = [_SkipOmitted(line) for line in actual_data.splitlines(True)]
+    expected_lines = [l.rstrip() for l in f_expected.readlines()]
+  actual_lines = [
+      _SkipOmitted(line).rstrip() for line in actual_data.splitlines()
+  ]
 
   if expected_lines == actual_lines:
     return None
@@ -53,9 +60,11 @@ def _DiffFileContents(expected_path, actual_data):
       actual_lines,
       fromfile=os.path.join('before', expected_path),
       tofile=os.path.join('after', expected_path),
-      n=0)
+      n=0,
+      lineterm='',
+  )
 
-  return ''.join(diff).rstrip()
+  return '\n'.join(diff)
 
 
 def AddCommandLineFlags(parser):