Mark JSArrayBuffer::SetupAllocatingData with WARN_UNUSED_RESULT.

Also update a call in cctest to check the result.

BUG=chromium:681843

Review-Url: https://codereview.chromium.org/2647573003
Cr-Commit-Position: refs/heads/master@{#42513}

src/objects.h

@@ -10838,10 +10838,12 @@ class JSArrayBuffer: public JSObject {
       void* data, size_t allocated_length,
       SharedFlag shared = SharedFlag::kNotShared);
 
-  static bool SetupAllocatingData(Handle<JSArrayBuffer> array_buffer,
-                                  Isolate* isolate, size_t allocated_length,
-                                  bool initialize = true,
-                                  SharedFlag shared = SharedFlag::kNotShared);
+  // Returns false if array buffer contents could not be allocated.
+  // In this case, |array_buffer| will not be set up.
+  static bool SetupAllocatingData(
+      Handle<JSArrayBuffer> array_buffer, Isolate* isolate,
+      size_t allocated_length, bool initialize = true,
+      SharedFlag shared = SharedFlag::kNotShared) WARN_UNUSED_RESULT;
 
   // Dispatched behavior.
   DECLARE_PRINTER(JSArrayBuffer)

test/cctest/heap/test-page-promotion.cc

@@ -115,7 +115,7 @@ UNINITIALIZED_TEST(PagePromotion_NewToNewJSArrayBuffer) {
     // Allocate a buffer we would like to check against.
     Handle<JSArrayBuffer> buffer =
         i_isolate->factory()->NewJSArrayBuffer(SharedFlag::kNotShared);
-    JSArrayBuffer::SetupAllocatingData(buffer, i_isolate, 100);
+    CHECK(JSArrayBuffer::SetupAllocatingData(buffer, i_isolate, 100));
     std::vector<Handle<FixedArray>> handles;
     // Simulate a full space, filling the interesting page with live objects.
     heap::SimulateFullSpace(heap->new_space(), &handles);