[tools] Simple turn-key utility to locally collect code coverage.

Collect code coverage by compiling for one or more target architectures
and then running tests, in the same directory. This way, gcov aggregates
results.

Bug: 
Change-Id: I3bf05416c535c0c566e48d4e73adc4eb49ba2793
Reviewed-on: https://chromium-review.googlesource.com/527522
Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46110}

tools/gcov.sh

+#!/bin/bash
+#
+# Copyright 2017 the V8 project authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# Build and collect code coverage data, cummulatively, on specified architectures.
+
+BUILD_TYPE=${BUILD_TYPE:-Release}
+
+declare -A modes=( [Release]=release [Debug]=debug )
+declare -A pairs=( [arm]=ia32 [arm64]=x64 [ia32]=ia32 [x64]=x64 )
+
+if [ -z ${modes[$BUILD_TYPE]} ]
+then
+    echo "BUILD_TYPE must be {<unspecified>|Release|Debug}"
+    echo "Release is default"
+    exit
+fi
+
+mode=${modes[$BUILD_TYPE]}
+
+echo "Using build:" $BUILD_TYPE
+v8_root=$(readlink -f $(dirname $BASH_SOURCE)/../)
+work_dir=$v8_root/cov
+build_dir=$work_dir/$BUILD_TYPE
+
+if [ -z $@ ]
+then
+    echo "Pass at least one target architecture"
+    echo "Supported architectures: x64 ia32 arm arm64"
+    echo ""
+    echo "Example: ./tools/gcov.sh x64 arm"
+    echo ""
+    echo "Optionally, set BUILD_TYPE env variable to"
+    echo "either Debug or Release, to use the corresponding build."
+    echo "By default, BUILD_TYPE is Release."
+    echo ""
+    echo "Example: BUILD_TYPE=Debug ./tools/gcov.sh x64 arm"
+    echo ""
+    exit
+fi
+
+lcov --directory=$build_dir --zerocounters
+
+# Mapping v8 build terminology to gnu compiler terminology:
+#   target_arch is the host, and
+#   v8_target_arch is the target
+
+for v8_target_arch in "$@"
+do
+    target_arch=${pairs[$v8_target_arch]}
+    if [ -z $target_arch ]
+    then
+        echo "Skipping unknown architecture: " $v8_target_arch
+    else
+        echo "Building" $v8_target_arch
+        GYP_DEFINES="component=static_library use_goma=1 target_arch=$target_arch v8_target_arch=$v8_target_arch coverage=1 clang=0" python $v8_root/gypfiles/gyp_v8.py -G output_dir=$work_dir
+        ninja -C $build_dir -j2000
+        $v8_root/tools/run-tests.py --gcov-coverage --arch=$v8_target_arch --mode=$mode --shell-dir=$build_dir --exhaustive-variants
+    fi
+done
+
+lcov --directory=$build_dir --capture --output-file $work_dir/app.info
+genhtml --output-directory $work_dir/html $work_dir/app.info
+echo "Done"
+echo "Output available at: " $work_dir/html/index.html