dump info is inaccurate and incomplete

[sigmundch]

ensure that when we tally every element in the output of dumpinfo, we can count 100% of the program size.

We've seen that for small apps, 10% is missing, it might be more for larger apps. So far pieces that are not included are:

• constants (fixed)
• lazily initialized top-levels and statics
• some portion of the dart2js setup boilerplate

[sigmundch]

Also, I've noticed some things might be counted twice, some things might be counted incorrectly.

Two examples I've noticed:

• counting code, when size was previously registered. See dump_info L126 - maybe that add operation should be guarded with if size != 0?
• adding more code than needed? In particular, dumpInfoTask.codeOf includes all code associated with an element. Are all those pieces present in the output and, thus, need to be counted?