Turn on warnings for usage of disabled V8 APIs

R=vogelheim@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1146933002
diff --git a/BUILD.gn b/BUILD.gn
index 00774dd..4074c75 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -19,6 +19,7 @@
     "_FPDFSDK_LIB",
     "_NO_GDIPLUS_",  # workaround text rendering issues on Windows
     "OPJ_STATIC",
+    "V8_DEPRECATION_WARNINGS",
   ]
 
   if (pdf_use_skia) {
diff --git a/build/standalone.gypi b/build/standalone.gypi
index 186db6e..c0eaef4 100644
--- a/build/standalone.gypi
+++ b/build/standalone.gypi
@@ -161,6 +161,10 @@
     'ldflags': [
       '-pthread',
     ],
+    'defines': [
+      # Don't use deprecated V8 APIs anywhere.
+      'V8_DEPRECATION_WARNINGS',
+    ],
     'msvs_cygwin_dirs': ['<(DEPTH)/v8/third_party/cygwin'],
     'msvs_configuration_attributes': {
       'OutputDirectory': '<(DEPTH)\\build\\$(ConfigurationName)',
@@ -283,4 +287,4 @@
     # See comment in Chromium's common.gypi for why this is needed.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   }
-}
\ No newline at end of file
+}