[heap] Enable concurrent marking on all platforms.

Bug: chromium:694255
Change-Id: Ie596e02207f13762dbfa77e4fe65950913302b47
Reviewed-on: https://chromium-review.googlesource.com/690075Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48227}

BUILD.gn

@@ -81,7 +81,7 @@ declare_args() {
   v8_enable_trace_ignition = false
 
   # Sets -dV8_CONCURRENT_MARKING
-  v8_enable_concurrent_marking = ""
+  v8_enable_concurrent_marking = true
 
   # Sets -dV8_CSA_WRITE_BARRIER
   v8_enable_csa_write_barrier = true
@@ -150,13 +150,6 @@ if (v8_enable_v8_checks == "") {
 if (v8_check_microtasks_scopes_consistency == "") {
   v8_check_microtasks_scopes_consistency = is_debug || dcheck_always_on
 }
-if (v8_enable_concurrent_marking == "") {
-  if (target_cpu == "x86" || target_cpu == "x64") {
-    v8_enable_concurrent_marking = true
-  } else {
-    v8_enable_concurrent_marking = false
-  }
-}
 
 # Specifies if the target build is a simulator build. Comparing target cpu
 # with v8 target cpu to not affect simulator builds for making cross-compile

gypfiles/features.gypi

@@ -82,13 +82,8 @@
     'v8_check_microtasks_scopes_consistency%': 'false',
 
     # Enable concurrent marking.
-    'conditions': [
-      ['target_arch=="x64" or target_arch=="ia32"', {
-        'v8_enable_concurrent_marking%': 1,
-      },{
-        'v8_enable_concurrent_marking%': 0,
-      }]
-    ],
+    'v8_enable_concurrent_marking%': 1,
+
     # Controls the threshold for on-heap/off-heap Typed Arrays.
     'v8_typed_array_max_size_in_heap%': 64,
   },