The process-wide memory usage statistics of sqlite library is added to
chrome://tracing. The memory usage of sqlite library is mainly through
sqlite_malloc. The total usage of the process is recorded by
sqlite3_memory_used() api. This CL also adds per-connection memory
usage to tracing. Each connection uses memory for cache, schema and
statement, and these usages are recorded. sqlit3_malloc uses malloc
internally to allocate memory. So, thie memory is traced as
sub-allocation from system_allocator(malloc).
This CL lets us keep track of sqlite memory usage in chrome telemetry.

BUG=466141

Review URL: https://codereview.chromium.org/1327063002

Cr-Commit-Position: refs/heads/master@{#353549}