Set DISCARDABLE_MEMORY_ALWAYS_SUPPORTED_NATIVELY to true on Android.

Also change render_process_visibility_manager to use
MEMORY_PRESSURE_MODERATE when the renderer loses visibility
since MEMORY_PRESSURE_CRITICAL should be reserved for
situations where memory pressure is really critical.

BUG=

Review URL: https://chromiumcodereview.appspot.com/18910002

git-svn-id: http://src.chromium.org/svn/trunk/src/build@211635 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -418,6 +418,12 @@
       # Managed users are enabled by default.
       'enable_managed_users%': 1,
 
+      # Platform natively supports discardable memory.
+      'native_discardable_memory%': 0,
+
+      # Platform sends memory pressure signals natively.
+      'native_memory_pressure_signals%': 0,
+
       'spdy_proxy_auth_origin%' : '',
       'spdy_proxy_auth_property%' : '',
       'spdy_proxy_auth_value%' : '',
@@ -514,6 +520,8 @@
           'remoting%': 0,
           'arm_neon%': 0,
           'arm_neon_optional%': 1,
+          'native_discardable_memory%': 1,
+          'native_memory_pressure_signals%': 1,
         }],
 
         # Enable autofill dialog for Android and Views-enabled platforms for now.
@@ -835,6 +843,8 @@
     'google_default_client_id%': '<(google_default_client_id)',
     'google_default_client_secret%': '<(google_default_client_secret)',
     'enable_managed_users%': '<(enable_managed_users)',
+    'native_discardable_memory%': '<(native_discardable_memory)',
+    'native_memory_pressure_signals%': '<(native_memory_pressure_signals)',
     'spdy_proxy_auth_origin%': '<(spdy_proxy_auth_origin)',
     'spdy_proxy_auth_property%': '<(spdy_proxy_auth_property)',
     'spdy_proxy_auth_value%': '<(spdy_proxy_auth_value)',
@@ -3417,6 +3427,12 @@
               '-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'],
+          }],
         ],
       },
     }],