Add partial magnifier to ash palette.

The partial magnifier will magnify a small portion of the screen, similar to a spyglass.

TEST=./out/Release/ash_unittests --gtest_filter=PartialMagnificationControllerTest.*
TBR=oshima@chromium.org

BUG=616112

Review-Url: https://codereview.chromium.org/2239553002
Cr-Commit-Position: refs/heads/master@{#414124}
void HandleLaunchLastApp() {
  base::RecordAction(UserMetricsAction("Accel_Launch_Last_App"));
  Shelf::ForPrimaryDisplay()->LaunchAppIndexAt(-1);
 }

void HandleLaunchLastApp() {
  base::RecordAction(UserMetricsAction("Accel_Launch_Last_App"));
  Shelf::ForPrimaryDisplay()->LaunchAppIndexAt(-1);
 }
