Add external/brotli to the manifest.

Bug: http://b/38121702
Test: builds
Change-Id: I35d3be22110be0167ede4771ec200fcfa8ac0f88

default.xml

@@ -90,6 +90,7 @@
   <project path="external/blktrace" name="platform/external/blktrace" groups="pdk" />
   <project path="external/boringssl" name="platform/external/boringssl" groups="pdk" />
   <project path="external/bouncycastle" name="platform/external/bouncycastle" groups="pdk" />
+  <project path="external/brotli" name="platform/external/brotli" groups="pdk" />
   <project path="external/bsdiff" name="platform/external/bsdiff" groups="pdk" />
   <project path="external/bzip2" name="platform/external/bzip2" groups="pdk" />
   <project path="external/c-ares" name="platform/external/c-ares" groups="pdk" />