Optimize ExtractSymbols (pprof).
Optimize ExtractSymbols (pprof).

Modify ExtractSymbols to operate on sorted PCs and libraries, in order
to reduce computational complexity from O(N*M) to O(N+M).

AndroidExternal/jemalloc,wespelee/jemalloc,CMRemix/android_external_jemalloc,glandium/jemalloc,sudosurootdev/external_jemalloc,sudosurootdev/external_jemalloc,TeamExodus/external_jemalloc,tempbottle/jemalloc,TeamExodus/external_jemalloc,android-ia/platform_external_jemalloc,percona/jemalloc-debian,vashstorm/jemalloc,flyfeifan/jemalloc,ahmetmircik/jemalloc,garoose/jemalloc,wespelee/jemalloc,tempbottle/jemalloc,kmiku7/jemalloc,xin3liang/platform_external_jemalloc,wespelee/jemalloc,cpeterso/jemalloc,yy-nm/jemalloc,Dmitry-Me/jemalloc,android-ia/platform_external_jemalloc,geekboxzone/lollipop_external_jemalloc,Snaipe/jemalloc,Dmitry-Me/jemalloc,splbio/jemalloc,CMRemix/android_external_jemalloc,wqfish/jemalloc,jemalloc/jemalloc-cmake,vashstorm/jemalloc,tempbottle/jemalloc,wfxiang08/jemalloc,shekkbuilder/jemalloc,glandium/jemalloc,cpeterso/jemalloc,lvfeng1130/jemalloc,kmiku7/jemalloc,geekboxzone/lollipop_external_jemalloc,shekkbuilder/jemalloc,geekboxzone/lollipop_external_jemalloc,geekboxzone/mmallow_external_jemalloc,CMRemix/android_external_jemalloc,leebaok/jemalloc-4.2.1-readcode,Snaipe/jemalloc,Dmitry-Me/jemalloc,wfxiang08/jemalloc,Snaipe/jemalloc,yy-nm/jemalloc,vashstorm/jemalloc,CyanogenMod/android_external_jemalloc,AndroidExternal/jemalloc,CyanogenMod/android_external_jemalloc,lilothar/jemalloc,Snaipe/jemalloc,flyfeifan/jemalloc,flyfeifan/jemalloc,kmiku7/jemalloc,lvfeng1130/jemalloc,splbio/jemalloc,garoose/jemalloc,tempbottle/jemalloc,percona/jemalloc-debian,sudosurootdev/external_jemalloc,awreece/jemalloc,lilothar/jemalloc,8l/jemalloc,CyanogenMod/android_external_jemalloc,dxq-git/jemalloc,VRToxin/android_external_jemalloc,lvfeng1130/jemalloc,xin3liang/platform_external_jemalloc,lvfeng1130/jemalloc,VRToxin/android_external_jemalloc,ahmetmircik/jemalloc,leebaok/jemalloc-4.2.1-readcode,awreece/jemalloc,8l/jemalloc,CMRemix/android_external_jemalloc,sudosurootdev/external_jemalloc,android-ia/platform_external_jemalloc,shekkbuilder/jemalloc,AndroidExternal/jemalloc,geekboxzone/mmallow_external_jemalloc,dxq-git/jemalloc,wqfish/jemalloc,wqfish/jemalloc,dxq-git/jemalloc,xin3liang/platform_external_jemalloc,yy-nm/jemalloc,android-ia/platform_external_jemalloc,percona/jemalloc-debian,jemalloc/jemalloc-cmake,leebaok/jemalloc-4.2.1-readcode,percona/jemalloc-debian,dcreager/jemalloc,garoose/jemalloc,AndroidExternal/jemalloc,glandium/jemalloc,lilothar/jemalloc,yy-nm/jemalloc,leebaok/jemalloc-4.2.1-readcode,vashstorm/jemalloc,jemalloc/jemalloc-cmake,geekboxzone/mmallow_external_jemalloc,Dmitry-Me/jemalloc,8l/jemalloc,wespelee/jemalloc,cpeterso/jemalloc,VRToxin/android_external_jemalloc,cpeterso/jemalloc,garoose/jemalloc,wqfish/jemalloc,flyfeifan/jemalloc,jemalloc/jemalloc-cmake,awreece/jemalloc,lilothar/jemalloc,geekboxzone/mmallow_external_jemalloc,dxq-git/jemalloc,xin3liang/platform_external_jemalloc,dcreager/jemalloc,wqfish/jemalloc,TeamExodus/external_jemalloc,splbio/jemalloc,geekboxzone/lollipop_external_jemalloc,TeamExodus/external_jemalloc,glandium/jemalloc,ahmetmircik/jemalloc,ahmetmircik/jemalloc,CyanogenMod/android_external_jemalloc,dcreager/jemalloc,VRToxin/android_external_jemalloc,shekkbuilder/jemalloc,awreece/jemalloc,wfxiang08/jemalloc,wfxiang08/jemalloc,kmiku7/jemalloc,8l/jemalloc