fuchsia: Disable use_v8_context_snapshot

Causing extra long compiles, and is currently of limited utility on
Fuchsia. We might want to investigate the runtime performance delta for
this feature once more complex JS is running on Fuchsia.

Bug: 764576, 807320
Change-Id: Iefee81a7e9078b42b68766f6891bbed2233a6599
Reviewed-on: https://chromium-review.googlesource.com/893427Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Scott Graham <scottmg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532989}

tools/v8_context_snapshot/v8_context_snapshot.gni

@@ -13,9 +13,10 @@ import("//v8/gni/v8.gni")
 
 declare_args() {
   # TODO(crbug.com/764576): Enable the feature on more environments.
-  use_v8_context_snapshot = !is_chromeos && !is_android && !is_chromecast &&
-                            !(host_os == "mac" && current_cpu == "x86") &&
-                            (v8_target_cpu == target_cpu || is_msan)
+  use_v8_context_snapshot =
+      !is_chromeos && !is_android && !is_chromecast && !is_fuchsia &&
+      !(host_os == "mac" && current_cpu == "x86") &&
+      (v8_target_cpu == target_cpu || is_msan)
 }
 
 # We cannot use V8 context snapshot, if V8 doesn't use snapshot files.