Updates Piex and uses it to obtain the DNG dimensions.

DEPS

Index: DEPS
diff --git a/DEPS b/DEPS
index aa54d15ebf9e23a22037b0fee75b2acd40bb9212..e0c098f3ba82f7a529fde1dedd419e27c944de19 100644
--- a/DEPS
+++ b/DEPS
@@ -22,7 +22,7 @@ deps = {
   "third_party/externals/giflib"  : "https://android.googlesource.com/platform/external/giflib.git@ab10e256df4f684260ca239905b1cec727181f6c",
 
   "third_party/externals/dng_sdk" : "https://android.googlesource.com/platform/external/dng_sdk.git@0baf877c64aeb9f5c5d0d3f13c8d2eb25a3c8837",
-  "third_party/externals/piex"    : "https://android.googlesource.com/platform/external/piex.git@a9540117cdd785b0dd75f8c4c28b278f86eb485c",
+  "third_party/externals/piex"    : "https://android.googlesource.com/platform/external/piex.git@8aac937ca7051396de370c9d90aeb2393a0dd08d",
 
   "third_party/externals/libjpeg-turbo"             : "https://skia.googlesource.com/third_party/libjpeg-turbo.git@36422d9e165a33914436068536772cc6ed1e7886",
   # libjpeg-turbo depends on yasm to compile .asm files