[find_dependencies.py] Explicitly exclude all files under python sys.…

…prefix.

When running the dependency finder under a VirtualEnv (such as vpython),
it will accidentally pick up dependencies from the sys.prefix.

Bug: 804174,818054
Change-Id: Ic6a677413ffed782ab49a772cc0eb73b7e8a87b2
Reviewed-on: https://chromium-review.googlesource.com/944899
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: David Tu <dtu@chromium.org>
Reviewed-by: Ned Nguyen <nednguyen@google.com>
Cr-Commit-Position: refs/heads/master@{#540459}

tools/perf/core/find_dependencies.py

@@ -44,6 +44,11 @@ def FindPythonDependencies(module_path):
   if modulegraph is None:
     raise import_error
 
+  prefixes = [sys.prefix]
+  if hasattr(sys, 'real_prefix'):
+    prefixes.append(sys.real_prefix)
+  logging.info('Excluding Prefixes: %r', prefixes)
+
   sys_path = sys.path
   sys.path = list(sys_path)
   try:
@@ -75,6 +80,10 @@ def FindPythonDependencies(module_path):
       if not path.IsSubpath(module_path, path_util.GetChromiumSrcDir()):
         continue
 
+      # Exclude any dependencies which exist in the python installation.
+      if any(path.IsSubpath(module_path, pfx) for pfx in prefixes):
+        continue
+
       yield module_path
       if node.packagepath is not None:
         for p in node.packagepath: