Fix generate_emma_html.py failing due to 0-length .em files

build/android/generate_emma_html.py

Index: build/android/generate_emma_html.py
diff --git a/build/android/generate_emma_html.py b/build/android/generate_emma_html.py
index 64d834f3383a86dd1109755baaaada3727242532..9d1d7330b3600ef74e7e9e72a995db5497b2b9b2 100755
--- a/build/android/generate_emma_html.py
+++ b/build/android/generate_emma_html.py
@@ -58,6 +58,9 @@ def main():
 
   coverage_files = _GetFilesWithExt(options.coverage_dir, 'ec')
   metadata_files = _GetFilesWithExt(options.metadata_dir, 'em')
+  # Filter out zero-length files. These are created by emma_instr.py when a
+  # target has no classes matching the coverage filter.
+  metadata_files = [f for f in metadata_files if os.path.getsize(f)]
   print 'Found coverage files: %s' % str(coverage_files)
   print 'Found metadata files: %s' % str(metadata_files)
 
@@ -87,6 +90,10 @@ def main():
     for f in coverage_files:
       os.remove(f)
 
+  # Command tends to exit with status 0 when it actually failed.
+  if not exit_code and not os.path.exists(options.output):
+    exit_code = 1
+
   return exit_code