Add discardable memory emulation for non-android/mac platforms

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 04c81e5731ba73b5558435e305ddb9fcb3bee899..45167a12ab456100a28a0772c0fa7cd51956c087 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -555,6 +555,11 @@
           'proprietary_codecs%': 0,
         }],
 
+        ['OS=="mac"', {
+          'native_discardable_memory%': 1,
+          'native_memory_pressure_signals%': 1,
+        }],
+
         # Enable autofill dialog for Android, Mac and Views-enabled platforms.
         ['toolkit_views==1 or (OS=="android" and android_webview_build==0) or OS=="mac"', {
           'enable_autofill_dialog%': 1
@@ -2049,6 +2054,12 @@
       ['enable_hidpi==1', {
         'defines': ['ENABLE_HIDPI=1'],
       }],
+      ['native_discardable_memory==1', {
+        'defines': ['DISCARDABLE_MEMORY_ALWAYS_SUPPORTED_NATIVELY'],
+      }],
+      ['native_memory_pressure_signals==1', {
+        'defines': ['SYSTEM_NATIVELY_SIGNALS_MEMORY_PRESSURE'],
+      }],
       ['fastbuild!=0', {
         'xcode_settings': {
           'GCC_GENERATE_DEBUGGING_SYMBOLS': 'NO',
@@ -3463,12 +3474,6 @@
               '-B<(PRODUCT_DIR)/../../third_party/gold',
             ],
           }],
-          ['native_discardable_memory', {
-            'defines': ['DISCARDABLE_MEMORY_ALWAYS_SUPPORTED_NATIVELY'],
-          }],
-          ['native_memory_pressure_signals', {
-            'defines': ['SYSTEM_NATIVELY_SIGNALS_MEMORY_PRESSURE'],
-          }],
         ],
       },
     }],