[wasm] Enable wasm threads by default in V8

Finer grained control of platforms that support threads are
enforced by chromium.

Bug: chromium:1167733
Change-Id: Ic34a4950aebf6ba394053b79df97b703af333636
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2810190Reviewed-by: Lutz Vahl <vahl@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Deepti Gandluri <gdeepti@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73919}

src/wasm/wasm-feature-flags.h

@@ -66,14 +66,6 @@
   /* Staged in v8.7 * */                                                       \
   V(return_call, "return call opcodes", false)                                 \
                                                                                \
-  /* Threads proposal. */                                                      \
-  /* https://github.com/webassembly/threads */                                 \
-  /* NOTE: This is enabled via chromium flag on desktop systems since v7.4  */ \
-  /* (see https://crrev.com/c/1487808). ITS: https://groups.google.com/a/   */ \
-  /* chromium.org/d/msg/blink-dev/tD6np-OG2PU/rcNGROOMFQAJ */                  \
-  /* V8 side owner: gdeepti */                                                 \
-  V(threads, "thread opcodes", false)                                          \
-                                                                               \
   /* Type reflection proposal. */                                              \
   /* https://github.com/webassembly/js-types */                                \
   /* V8 side owner: ahaas */                                                   \
@@ -96,8 +88,19 @@
   /* V8 side owner: gdeepti, zhin */                                           \
   /* Staged in v8.7 * */                                                       \
   /* Shipped in v9.1 * */                                                      \
-  V(simd, "SIMD opcodes", true)
-
+  V(simd, "SIMD opcodes", true)                                                \
+                                                                               \
+  /* Threads proposal. */                                                      \
+  /* https://github.com/webassembly/threads */                                 \
+  /* NOTE: This is enabled via chromium flag on desktop systems since v7.4, */ \
+  /* and on android from 9.1. Threads are only available when */               \
+  /* SharedArrayBuffers are enabled as well, and are gated by COOP/COEP */     \
+  /* headers, more fine grained control is in the chromium codebase */         \
+  /* ITS: https://groups.google.com/a/chromium.org/d/msg/blink-dev/ */         \
+  /* tD6np-OG2PU/rcNGROOMFQAJ */                                               \
+  /* V8 side owner: gdeepti */                                                 \
+  V(threads, "thread opcodes", true)                                           \
+                                                                               \
 // Combination of all available wasm feature flags.
 #define FOREACH_WASM_FEATURE_FLAG(V)        \
   FOREACH_WASM_EXPERIMENTAL_FEATURE_FLAG(V) \