Fix Clang style-plugin errors in memory_pressure component
From http://build.chromium.org/p/chromium.fyi/builders/CrWinClang/builds/2796/steps/compile/logs/stdio:
..\..\components/memory_pressure/filtered_memory_pressure_calculator.h(31,3) :
error: [chromium-style] Complex destructor has an inline body.
~FilteredMemoryPressureCalculator() {}
^
..\..\components/memory_pressure/filtered_memory_pressure_calculator.h(31,39) :
error: [chromium-style] Overriding method must be marked with 'override' or 'final'.
~FilteredMemoryPressureCalculator() {}
^
override
..\..\components/memory_pressure/direct_memory_pressure_calculator.h(41,45) :
error: [chromium-style] Overriding method must be marked with 'override' or 'final'.
virtual ~DirectMemoryPressureCalculator() {}
^
override
BUG=82385, 520962
TBR=chrisha
Review URL: https://codereview.chromium.org/1314553003 .
Cr-Commit-Position: refs/heads/master@{#345121}
3 files changed
