cc: Simplify the presubmit regex used to identify paths and files.

This [\\/] should account for both Windows \ and Posix /.

BUG=None
TEST=git cl presubmit -uv
R=danakj@chromium.org

Review URL: https://codereview.chromium.org/892743002

Cr-Commit-Position: refs/heads/master@{#314145}

cc/PRESUBMIT.py

@@ -11,7 +11,7 @@ for more details about the presubmit API built into depot_tools.
 import re
 import string
 
-CC_SOURCE_FILES=(r'^cc/.*\.(cc|h)$', r'^cc\\.*\.(cc|h)$')
+CC_SOURCE_FILES=(r'^cc[\\/].*\.(cc|h)$',)
 
 def CheckChangeLintsClean(input_api, output_api):
   input_api.cpplint._cpplint_state.ResetErrorCounts()  # reset global state