Re-land r296395: "Instrumented libraries: update the libnspr4 build script."

There has been a security update in gPrecise which changed the paths somewhat.
The previous version of this CL was reverted as it broke on vanilla Precise.
This version fixes that.

BUG=313751
TBR=glider@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/602823002

Cr-Commit-Position: refs/heads/master@{#296466}

third_party/instrumented_libraries/scripts/libnspr4.sh

@@ -5,4 +5,13 @@
 
 # This script does some preparations before build of instrumented libnspr4.
 
-mv mozilla/nsprpub/* .
+if [ -d nspr ]
+then
+  mv nspr/* .
+elif [ -d mozilla/nsprpub ]
+then
+  mv mozilla/nsprpub/* .
+else
+  echo "libnspr4.sh: package has unexpected directory structure. Please update this script."
+  return 1
+fi