Add leakcanary to DEPS and third_party

DEPS

 # This file is used to manage the dependencies of the Chromium src repo. It is
 # used by gclient to determine what version of each dependency to check out, and
 # where.
 #
 # For more information, please refer to the official documentation:
 #   https://sites.google.com/a/chromium.org/dev/developers/how-tos/get-the-code
 #
 # When adding a new dependency, please update the top-level .gitignore file
 # to list the dependency's destination directory.
 #
@@ skipping 474 matching lines @@
 
     'src/third_party/netty4/src':
       Var('chromium_git') + '/external/netty4.git' + '@' + 'e0f26303b4ce635365be19414d0ac81f2ef6ba3c',
 
     'src/third_party/robolectric/lib':
       Var('chromium_git') + '/chromium/third_party/robolectric.git' + '@' + '6b63c99a8b6967acdb42cbed0adb067c80efc810',
 
     'src/third_party/ub-uiautomator/lib':
       Var('chromium_git') + '/chromium/third_party/ub-uiautomator.git' + '@' + '00270549ce3161ae72ceb24712618ea28b4f9434',
 
+    'src/third_party/leakcanary/src':
+      Var('chromium_git') + '/external/github.com/square/leakcanary.git' + '@' + '608ded739e036a3aa69db47ac43777dcee506f8e',
+
     'src/third_party/lss':
       Var('chromium_git') + '/external/linux-syscall-support/lss.git' + '@' + Var('lss_revision'),
 
     'src/third_party/requests/src':
       Var('chromium_git') + '/external/github.com/kennethreitz/requests.git' + '@' + 'f172b30356d821d180fa4ecfa3e71c7274a32de4',
 
     'src/third_party/custom_tabs_client/src':
       Var('chromium_git') + '/external/github.com/GoogleChrome/custom-tabs-client.git' + '@' + '592e63122055d37e58cd37bd89a973eed98340ef',
   },
 }
@@ skipping 324 matching lines @@
         'src/tools',
     ],
   },
   {
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     'name': 'gyp',
     'pattern': '.',
     'action': ['python', 'src/build/gyp_chromium'],
   },
 ]