Re-land: base: Replace PurgeAndTruncate with Shrink function.

build/common.gypi

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 588 matching lines @@
       'test_isolation_outdir%': '',
 
       'wix_path%': '<(DEPTH)/third_party/wix',
 
       # Supervised users are enabled by default.
       'enable_supervised_users%': 1,
 
       # Platform sends memory pressure signals natively.
       'native_memory_pressure_signals%': 0,
 
+      # Platform supports shrinking of discardable shared memory segments.
+      'discardable_shared_memory_shrinking%': 0,
+
       'spdy_proxy_auth_property%' : '',
       'spdy_proxy_auth_value%' : '',
       'enable_mdns%' : 0,
       'enable_service_discovery%': 0,
       'enable_wifi_bootstrapping%': 0,
       'enable_hangout_services_extension%': 0,
 
        # Enable the Syzygy optimization step.
       'syzygy_optimize%': 0,
 
@@ skipping 151 matching lines @@
         ['OS=="android" or branding=="Chrome" or chromecast==1', {
           'proprietary_codecs%': 1,
         }, {
           'proprietary_codecs%': 0,
         }],
 
         ['OS=="mac" or OS=="ios"', {
           'native_memory_pressure_signals%': 1,
         }],
 
+        ['OS!="win" and OS!="android"', {
+          'discardable_shared_memory_shrinking%': 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,
 
           'conditions': [
             ['buildtype=="Official"', {
               'enable_prod_wallet_service%': 1,
             }],
           ]
         }],
@@ skipping 401 matching lines @@
     'gyp_managed_install%': 0,
     'create_standalone_apk%': 1,
     'enable_app_list%': '<(enable_app_list)',
     'use_default_render_theme%': '<(use_default_render_theme)',
     'enable_settings_app%': '<(enable_settings_app)',
     'google_api_key%': '<(google_api_key)',
     'google_default_client_id%': '<(google_default_client_id)',
     'google_default_client_secret%': '<(google_default_client_secret)',
     'enable_supervised_users%': '<(enable_supervised_users)',
     'native_memory_pressure_signals%': '<(native_memory_pressure_signals)',
+    'discardable_shared_memory_shrinking%': '<(discardable_shared_memory_shrinking)',
     'spdy_proxy_auth_property%': '<(spdy_proxy_auth_property)',
     'spdy_proxy_auth_value%': '<(spdy_proxy_auth_value)',
     'enable_mdns%' : '<(enable_mdns)',
     'enable_service_discovery%' : '<(enable_service_discovery)',
     'enable_wifi_bootstrapping%': '<(enable_wifi_bootstrapping)',
     'enable_hangout_services_extension%' : '<(enable_hangout_services_extension)',
     'v8_optimized_debug%': '<(v8_optimized_debug)',
     'proprietary_codecs%': '<(proprietary_codecs)',
     'use_goma%': '<(use_goma)',
     'gomadir%': '<(gomadir)',
@@ skipping 1497 matching lines @@
       }],
       ['notifications==1', {
         'defines': ['ENABLE_NOTIFICATIONS'],
       }],
       ['enable_hidpi==1', {
         'defines': ['ENABLE_HIDPI=1'],
       }],
       ['native_memory_pressure_signals==1', {
         'defines': ['SYSTEM_NATIVELY_SIGNALS_MEMORY_PRESSURE'],
       }],
+      ['discardable_shared_memory_shrinking==1', {
+        'defines': ['DISCARDABLE_SHARED_MEMORY_SHRINKING'],
+      }],
       ['use_udev==1', {
         'defines': ['USE_UDEV'],
       }],
       ['fastbuild!=0', {
         'xcode_settings': {
           'GCC_GENERATE_DEBUGGING_SYMBOLS': 'NO',
         },
         'conditions': [
           ['OS=="win" and fastbuild==2', {
             # Completely disable debug information.
@@ skipping 3295 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }