Fix frame_editing_unittest.cc
Fix frame_editing_unittest.cc

The test fails since it's assuming out/testfile.yuv exists when running the test. Just opening the file at a later time than the SetUp function seems to break the test so that's not a viable solution. This CL uses a simple workaround that simply truncates the file before opening it, which works.

BUG=none
TEST=tools_unittests in Debug+Release on Mac, Win and Linux + memcheck, tsan, asan.

Review URL: https://webrtc-codereview.appspot.com/1067004

git-svn-id: 03ae4fbe531b1eefc9d815f31e49022782c42458@3401 4adac7df-926f-26a2-2b94-8c16560cd09d

android-ia/platform_external_chromium_org_third_party_webrtc,Omegaphora/external_chromium_org_third_party_webrtc,MIPS/external-chromium_org-third_party-webrtc,geekboxzone/lollipop_external_chromium_org_third_party_webrtc,android-ia/platform_external_chromium_org_third_party_webrtc,geekboxzone/lollipop_external_chromium_org_third_party_webrtc,Omegaphora/external_chromium_org_third_party_webrtc,MIPS/external-chromium_org-third_party-webrtc,Omegaphora/external_chromium_org_third_party_webrtc,jgcaaprom/android_external_chromium_org_third_party_webrtc,MIPS/external-chromium_org-third_party-webrtc,jgcaaprom/android_external_chromium_org_third_party_webrtc,MIPS/external-chromium_org-third_party-webrtc,geekboxzone/lollipop_external_chromium_org_third_party_webrtc,android-ia/platform_external_chromium_org_third_party_webrtc,android-ia/platform_external_chromium_org_third_party_webrtc,android-ia/platform_external_chromium_org_third_party_webrtc,geekboxzone/lollipop_external_chromium_org_third_party_webrtc,android-ia/platform_external_chromium_org_third_party_webrtc,jgcaaprom/android_external_chromium_org_third_party_webrtc,jgcaaprom/android_external_chromium_org_third_party_webrtc,MIPS/external-chromium_org-third_party-webrtc,Omegaphora/external_chromium_org_third_party_webrtc,jgcaaprom/android_external_chromium_org_third_party_webrtc,MIPS/external-chromium_org-third_party-webrtc,jgcaaprom/android_external_chromium_org_third_party_webrtc,Omegaphora/external_chromium_org_third_party_webrtc,jgcaaprom/android_external_chromium_org_third_party_webrtc,Omegaphora/external_chromium_org_third_party_webrtc,MIPS/external-chromium_org-third_party-webrtc,geekboxzone/lollipop_external_chromium_org_third_party_webrtc,android-ia/platform_external_chromium_org_third_party_webrtc,geekboxzone/lollipop_external_chromium_org_third_party_webrtc,geekboxzone/lollipop_external_chromium_org_third_party_webrtc,geekboxzone/lollipop_external_chromium_org_third_party_webrtc,Omegaphora/external_chromium_org_third_party_webrtc,android-ia/platform_external_chromium_org_third_party_webrtc,MIPS/external-chromium_org-third_party-webrtc,Omegaphora/external_chromium_org_third_party_webrtc,jgcaaprom/android_external_chromium_org_third_party_webrtc