Add counter for new shared/array buffers that fail to allocate space.

Records histogram of ArrayBuffer/SharedArrayBuffer new allocations
that failed because it couldn't allocate space for the
buffer. Histogram is based on the buffer size requested.

This counter is intended to give some clue as to how often, and what sizes are being requested. Unfortunately, the how often can't be answered with the current counter. The problem is that V8 doesn't currently support this possibility yet. Hence, for now, introducing a counter that at least counts the number/size of failing requests.

BUG=chromium:704922
R=bbudge@chromium.org,bradnelson@chromium.org,mtrofin@chromium.org

Review-Url: https://codereview.chromium.org/2786913004
Cr-Commit-Position: refs/heads/master@{#44318}

src/counters.h

@@ -929,7 +929,8 @@ class RuntimeCallTimerScope {
      51)                                                                      \
   HR(wasm_functions_per_wasm_module, V8.WasmFunctionsPerModule.wasm, 1,       \
      100000, 51)                                                              \
-  HR(array_buffer_big_allocations, V8.ArrayBufferBigAllocations, 1, 32, 32)
+  HR(array_buffer_big_allocations, V8.ArrayBufferBigAllocations, 1, 32, 32)   \
+  HR(array_buffer_new_size_failures, V8.ArrayBufferNewSizeFailures, 1, 32, 32)
 
 #define HISTOGRAM_TIMER_LIST(HT)                                               \
   /* Garbage collection timers. */                                             \

src/objects.cc

@@ -19485,7 +19485,12 @@ bool JSArrayBuffer::SetupAllocatingData(Handle<JSArrayBuffer> array_buffer,
       data = isolate->array_buffer_allocator()->AllocateUninitialized(
           allocated_length);
     }
-    if (data == NULL) return false;
+    if (data == NULL) {
+      isolate->counters()->array_buffer_new_size_failures()->AddSample(
+          sizeof(uint64_t) * kBitsPerByte -
+          base::bits::CountLeadingZeros64(allocated_length));
+      return false;
+    }
   } else {
     data = NULL;
   }