Support code coverage.

build/standalone.gypi

Index: build/standalone.gypi
diff --git a/build/standalone.gypi b/build/standalone.gypi
index 400694486c5c42af314f2f350abc28bc6e1ffcef..e4935dee0c2ecac946ff9df575421670d4e15026 100644
--- a/build/standalone.gypi
+++ b/build/standalone.gypi
@@ -102,6 +102,10 @@
       # If no gomadir is set, it uses the default gomadir.
       'use_goma%': 0,
       'gomadir%': '',
+
+      # Instrument for code coverage with gcov.
+      'coverage%': 0,
+
       'conditions': [
         # Set default gomadir.
         ['OS=="win"', {
@@ -132,6 +136,11 @@
         }, {
           'test_isolation_mode%': 'noop',
         }],
+
+        ['coverage==1', {
+          'host_clang%': '0',
+          'clang%': 0,
+        }],
       ],
     },
     'base_dir%': '<(base_dir)',
@@ -155,6 +164,7 @@
     'cfi_diag%': '<(cfi_diag)',
     'cfi_blacklist%': '<(cfi_blacklist)',
     'test_isolation_mode%': '<(test_isolation_mode)',
+    'coverage%': '<(coverage)',
 
     # Add a simple extras solely for the purpose of the cctests
     'v8_extra_library_files': ['../test/cctest/test-extra.js'],
@@ -679,6 +689,10 @@
           [ 'component=="shared_library"', {
             'cflags': [ '-fPIC', ],
           }],
+          [ 'coverage==1', {
+            'cflags': [ '-fprofile-arcs', '-ftest-coverage', '-O0'],
+            'ldflags': [ '-fprofile-arcs'],
+          }],
         ],
       },
     }],