Fix a bug in the destruction of BenchmarkFamilies.
Fix a bug in the destruction of BenchmarkFamilies.

subailong/benchmark,gezidan/benchmark,gezidan/benchmark,Photonomie/benchmark,subailong/benchmark,ntx-/benchmark,everbase/benchmark,xlqian/benchmark,nickhutchinson/benchmark-cxx03,efcs/benchmark,nickhutchinson/benchmark,fuchsia-mirror/third_party-benchmark,google/benchmark,nickhutchinson/benchmark,mockingbirdnest/benchmark,quantumsteve/benchmark,LepelTsmok/benchmark,codygray/benchmark,codygray/benchmark,disconnect3d/benchmark,ntx-/benchmark,LepelTsmok/benchmark,bowlofstew/benchmark,subailong/benchmark,bowlofstew/benchmark,everbase/benchmark,fuchsia-mirror/third_party-benchmark,everbase/benchmark,fuchsia-mirror/third_party-benchmark,google/benchmark,bowlofstew/benchmark,quantumsteve/benchmark,disconnect3d/benchmark,chemhack/benchmark,xlqian/benchmark,nickhutchinson/benchmark,mockingbirdnest/benchmark,disconnect3d/benchmark,chemhack/benchmark,google/benchmark,nickhutchinson/benchmark-cxx03,disconnect3d/benchmark,subailong/benchmark,xlqian/benchmark,quantumsteve/benchmark,nickhutchinson/benchmark-cxx03,chemhack/benchmark,eliben/benchmark,Photonomie/benchmark,nickhutchinson/benchmark,gezidan/benchmark,chandlerc/benchmark,Photonomie/benchmark,xlqian/benchmark,LepelTsmok/benchmark,nickhutchinson/benchmark-cxx03,efcs/benchmark,eliben/benchmark,chandlerc/benchmark,chandlerc/benchmark,Photonomie/benchmark,ntx-/benchmark,eliben/benchmark,bowlofstew/benchmark,quantumsteve/benchmark,ntx-/benchmark,efcs/benchmark,efcs/benchmark,chemhack/benchmark,eliben/benchmark,mockingbirdnest/benchmark,LepelTsmok/benchmark,mockingbirdnest/benchmark,chandlerc/benchmark,codygray/benchmark,fuchsia-mirror/third_party-benchmark,codygray/benchmark,gezidan/benchmark,everbase/benchmark