[Android] Add support for standalone PDFium gn build on Android.

DEPS

 use_relative_paths = True
 
 vars = {
   'chromium_git': 'https://chromium.googlesource.com',
   'pdfium_git': 'https://pdfium.googlesource.com',
 
-  'build_revision': '4842479bd8da7b9e5eb027f8c15bee533f9c328f',
+  'android_ndk_revision': '5022f40f12953c02b2614c5f7beb981ec5d0e833',
+  'build_revision': '9bbfcd5cce0290376e46f3aeaca3475e96a67fdb',
   'buildtools_revision': '099f1da55bfe8caa12266371a7eb983698fb1d87',
+  'catapult_revision': '8ff23141e1df724317e9f558644ce2a7d8afde54',
   'clang_revision': 'b6f620b311665e2d96d0921833f54295b9bbf925',
   'cygwin_revision': 'c89e446b273697fadf3a10ff1007a97c0b7de6df',
   'gen_library_loader_revision': '916d4acd8b2cde67a390737dfba90b3c37de23a1',
   'gmock_revision': '29763965ab52f24565299976b936d1265cb6a271',
   'gtest_revision': '8245545b6dc9c4703e6496d1efd19e975ad2b038',
   'icu_revision': 'c291cde264469b20ca969ce8832088acb21e0c48',
   'pdfium_tests_revision': '6c769320872e6ca82da4adaec1a497237f71b543',
   'skia_revision': '7942f22c607caf826a6a609b89338a569d0a30e7',
   'tools_memory_revision': '427f10475e1a8d72424c29d00bf689122b738e5d',
   'trace_event_revision': '54b8455be9505c2cb0cf5c26bb86739c236471aa',
@@ skipping 38 matching lines @@
 
   "v8":
     Var('chromium_git') + "/v8/v8.git@" + Var('v8_revision'),
 
   "v8/base/trace_event/common":
     Var('chromium_git') + "/chromium/src/base/trace_event/common.git@" +
         Var('trace_event_revision'),
 }
 
 deps_os = {
+  "android": {
+    "third_party/android_ndk":
+      Var('chromium_git') + "/android_ndk.git@" + Var('android_ndk_revision'),
+    "third_party/catapult":
+      Var('chromium_git') + "/external/github.com/catapult-project/catapult.git@" + Var('catapult_revision'),
+  },
   "win": {
     "v8/third_party/cygwin":
       Var('chromium_git') + "/chromium/deps/cygwin@" + Var('cygwin_revision'),
   },
 }
 
 include_rules = [
   # Basic stuff that everyone can use.
   # Note: public is not here because core cannot depend on public.
   '+testing',
@@ skipping 102 matching lines @@
                '--if-needed'
     ],
   },
   {
     # Update the Windows toolchain if necessary.
     'name': 'win_toolchain',
     'pattern': '.',
     'action': ['python', 'pdfium/build/vs_toolchain.py', 'update'],
   },
 ]