Don't apply pointer multipler to heap sizes on Android.

Don't apply pointer multipler to heap sizes on Android.

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}