Reduce time JavaScript is allowed to execute for from 12 to seven seconds

Do this to reduce the likelihood of running out of time before
finishing with the corpus on ClusterFuzz.

TBR=mmoroz@chromium.org

Bug: 791052
Change-Id: I8c91dc0ff3e64dbde9bc6e5b17ef85e456c64911
Reviewed-on: https://chromium-review.googlesource.com/803894Reviewed-by: Jonathan Metzman <metzman@chromium.org>
Reviewed-by: Abhishek Arya <inferno@chromium.org>
Commit-Queue: Jonathan Metzman <metzman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520965}

testing/libfuzzer/fuzzers/v8_fuzzer.cc

@@ -27,7 +27,7 @@ static const seconds kSleepSeconds(1);
 // kSleepSeconds + kMaxExecutionSeconds.
 // TODO(metzman): Determine if having such a short timeout causes too much
 // indeterminism.
-static const seconds kMaxExecutionSeconds(12);
+static const seconds kMaxExecutionSeconds(7);
 
 // Inspired by/copied from d8 code, this allocator will return nullptr when
 // an allocation request is made that puts currently_allocated_ over
@@ -153,11 +153,11 @@ extern "C" int LLVMFuzzerInitialize(int* argc, char*** argv) {
 }
 
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  static Environment* env = new Environment();
+
   if (size < 1)
     return 0;
 
-  static Environment* env = new Environment();
-
   v8::Isolate::Scope isolate_scope(env->isolate);
   v8::HandleScope handle_scope(env->isolate);
   v8::Local<v8::Context> context = v8::Context::New(env->isolate);