Pre-emptively add an (unused) #define for record-time filter scaling.

This will be used in Blink to protect the old implementation of hiDPI
filter scaling. Once CC has been taught how to apply hiDPI to filters,
the Blink implementation will be switched off at the same time by
removing this #define.

BUG=281516

Review URL: https://codereview.chromium.org/182863007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255580 0039d316-1c4b-4281-b951-d872f2087c98

build/common.gypi

@@ -2135,6 +2135,8 @@
     'defines': [
       # Don't use deprecated V8 APIs anywhere.
       'V8_DEPRECATION_WARNINGS',
+      # Temporary suppression until Blink code can be removed.
+      'BLINK_SCALE_FILTERS_AT_RECORD_TIME',
     ],
     'conditions': [
       ['(OS=="mac" or OS=="ios") and asan==1', {