Now that we no longer require AllocationInfo::limit to be aligned [1], we can do
more accurate inline-allocation-observation. This lets us get notified when the
next allocation that crosses the step-size boundary is allocated.

Fixed the test-cases. They make significantly more sense now given the step
sizes and the number of times we get notifications. For example, with a step
size of 512, an allocation of 16kb results in 32 notifications instead of 30
now.

[1] https://codereview.chromium.org/1444883003

R=hpayer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1448913003

Cr-Commit-Position: refs/heads/master@{#32091}