[Coverage] Minor fixes in coverage script.

This CL:
1. Updates out-dated comments about component build.
2. Makes sure logging is configured before it is called, otherwise, all
logs will be eaten.

Change-Id: Ibe3a162f55e0ab5dbf38ce33e0e192d79bb1057b
Reviewed-on: https://chromium-review.googlesource.com/1054345Reviewed-by: Abhishek Arya <inferno@chromium.org>
Reviewed-by: Max Moroz <mmoroz@chromium.org>
Commit-Queue: Yuke Liao <liaoyuke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557675}

tools/code_coverage/coverage.py

@@ -11,10 +11,6 @@
   "use_clang_coverage=true" and "is_component_build=false" GN flags to args.gn
   file in your build output directory (e.g. out/coverage).
 
-  Existing implementation requires "is_component_build=false" flag because
-  coverage info for dynamic libraries may be missing and "is_component_build"
-  is set to true by "is_debug" unless it is explicitly set to false.
-
   Example usage:
 
   gn gen out/coverage --args='use_clang_coverage=true is_component_build=false'
@@ -489,7 +485,6 @@ def DownloadCoverageToolsIfNeeded():
   try:
     clang_update.DownloadAndUnpack(coverage_tools_url,
                                    clang_update.LLVM_BUILD_DIR)
-    logging.info('Coverage tools %s unpacked.', package_version)
     with open(coverage_revision_stamp_file, 'w') as file_handle:
       file_handle.write('%s,%s' % (package_version, host_platform))
       file_handle.write('\n')