Fix buffer overflow error on buffer resize.
Fix buffer overflow error on buffer resize.

We were using the new, larger size for our buffer data copy step,
instead of the old, smaller size. This bug was causing a crash on
older nVidia drivers during normal browser usage.

Reproducible with the index-validation-large-buffer WebGL test.

BUG=angle:667
BUG=384420

Change-Id: I98ee893e0d8ba0bfc9adfe5a338da9b940248879
Reviewed-on: https://chromium-review.googlesource.com/203776
Tested-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Reviewed-by: Shannon Woods <0f3694938fd5703bd548127ee497e4d604509bef@chromium.org>
Reviewed-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/207122
Reviewed-by: Nicolas Capens <0612353e1fcebbfd4b302d9337447ca0cdfa9122@chromium.org>

jgcaaprom/android_external_chromium_org_third_party_angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,android-ia/platform_external_chromium_org_third_party_angle,MIPS/external-chromium_org-third_party-angle,android-ia/platform_external_chromium_org_third_party_angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,MIPS/external-chromium_org-third_party-angle,android-ia/platform_external_chromium_org_third_party_angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,jgcaaprom/android_external_chromium_org_third_party_angle,jgcaaprom/android_external_chromium_org_third_party_angle,geekboxzone/lollipop_external_chromium_org_third_party_angle,MIPS/external-chromium_org-third_party-angle,MIPS/external-chromium_org-third_party-angle,jgcaaprom/android_external_chromium_org_third_party_angle,android-ia/platform_external_chromium_org_third_party_angle