Update from https://crrev.com/305340

build/android/pylib/constants.py

Index: build/android/pylib/constants.py
diff --git a/build/android/pylib/constants.py b/build/android/pylib/constants.py
index 29da601259ddb734145583b41ca4e390fc75990e..e89a29869f9cd426a8a30f396b15b831cef3e84f 100644
--- a/build/android/pylib/constants.py
+++ b/build/android/pylib/constants.py
@@ -187,6 +187,7 @@ PYTHON_UNIT_TEST_SUITES = {
     'path': os.path.join(DIR_SOURCE_ROOT, 'build', 'android'),
     'test_modules': [
       'pylib.device.device_utils_test',
+      'pylib.utils.md5sum_test',
     ]
   },
   'gyp_py_unittests': {
@@ -246,8 +247,21 @@ def _Memoize(func):
   return Wrapper
 
 
-@_Memoize
+def SetAdbPath(adb_path):
+  os.environ['ADB_PATH'] = adb_path
+
+
 def GetAdbPath():
+  # Check if a custom adb path as been set. If not, try to find adb
+  # on the system.
+  if os.environ.get('ADB_PATH'):
+    return os.environ.get('ADB_PATH')
+  else:
+    return _FindAdbPath()
+
+
+@_Memoize
+def _FindAdbPath():
   if os.environ.get('ANDROID_SDK_ROOT'):
     return 'adb'
   # If envsetup.sh hasn't been sourced and there's no adb in the path,
@@ -260,7 +274,6 @@ def GetAdbPath():
     logging.debug('No adb found in $PATH, fallback to checked in binary.')
     return os.path.join(ANDROID_SDK_ROOT, 'platform-tools', 'adb')
 
-
 # Exit codes
 ERROR_EXIT_CODE = 1
 WARNING_EXIT_CODE = 88