[wasm] Turn on streaming compilation

I tested it with 30000 tests in the wasm spec test suite, and they all
pass.

Change-Id: Ice0fb64f56685f67521431213e3fc8fbc263750e
Reviewed-on: https://chromium-review.googlesource.com/822111Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50026}

src/flag-definitions.h

@@ -488,7 +488,7 @@ DEFINE_BOOL(wasm_trace_serialization, false,
             "trace serialization/deserialization")
 DEFINE_BOOL(wasm_async_compilation, true,
             "enable actual asynchronous compilation for WebAssembly.compile")
-DEFINE_BOOL(wasm_stream_compilation, false,
+DEFINE_BOOL(wasm_stream_compilation, true,
             "enable streaming compilation for WebAssembly")
 DEFINE_IMPLICATION(wasm_stream_compilation, wasm_async_compilation)
 DEFINE_BOOL(wasm_test_streaming, false,