Update V8 to Version 3.29.88.18

This is a cherry-pick of v8
https://chromium.googlesource.com/v8/v8/+/f0158730a3b758d746287cacc315ae262b83232d
to move from 3.29.88.17 to 3.29.88.18. This change only affects MIPS arch.

Original commit message:
Merged 3758fceca935f3307e2301984399497388574a70
Merged 61c0aa96e3d32b80e51ecfe7221a3dbc44f69746

MIPS: Improve runtime detection and compatibility wrt arch. revisions.

MIPS: Resolve chromium and android webview build conflicts.

BUG=
R=jkummerow@chromium.org, machenbach@chromium.org

Review URL: https://codereview.chromium.org/766273004

Change-Id: I941381d7c95c7ed61292b8f1cd64b0b9073cecdc
Cr-Commit-Position: refs/branch-heads/3.29@{#25234}
diff --git a/build/standalone.gypi b/build/standalone.gypi
index b09122b..32ad028 100644
--- a/build/standalone.gypi
+++ b/build/standalone.gypi
@@ -127,6 +127,16 @@
     'arm_fpu%': 'vfpv3',
     'arm_float_abi%': 'default',
     'arm_thumb': 'default',
+
+    # Default MIPS variable settings.
+    'mips_arch_variant%': 'r2',
+    # Possible values fp32, fp64, fpxx.
+    # fp32 - 32 32-bit FPU registers are available, doubles are placed in
+    #        register pairs.
+    # fp64 - 32 64-bit FPU registers are available.
+    # fpxx - compatibility mode, it chooses fp32 or fp64 depending on runtime
+    #        detection
+    'mips_fpu_mode%': 'fp32',
   },
   'target_defaults': {
     'variables': {