Android doesn't have swap space so if the heap goes over the physical memory
size the system will just kill us. Applying the Heap::kPointerMultipler
to heap size could cause the max heap size to be larger than physical memory.
Instead use the defaults which are based on actual physical memory configured
by Api::ConfigureDefaults().

BUG=432909
LOG=N

Review URL: https://codereview.chromium.org/960213007

Cr-Commit-Position: refs/heads/master@{#26954}