Add scripts for running LLVM coverage

gyp/common_conditions.gypi

 # Copyright 2015 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # conditions used in both common.gypi and skia.gyp in chromium
 #
 {
   'defines': [
     'SK_ALLOW_STATIC_GLOBAL_INITIALIZERS=<(skia_static_initializers)',
@@ skipping 390 matching lines @@
     }],
 
     [ 'skia_os in ["linux", "freebsd", "openbsd", "solaris", "chromeos"]',
       {
         'defines': [
           'SK_SAMPLES_FOR_X',
           'SK_BUILD_FOR_UNIX',
         ],
         'configurations': {
           'Coverage': {
-            'cflags': ['--coverage'],
-            'ldflags': ['--coverage'],
+            'conditions': [
+              [ 'skia_clang_build', {
+                'cflags': ['-fprofile-instr-generate', '-fcoverage-mapping'],
+                'ldflags': ['-fprofile-instr-generate', '-fcoverage-mapping'],
+              }, {
+                'cflags': ['--coverage'],
+                'ldflags': ['--coverage'],
+              }],
+            ],
           },
           'Debug': {
           },
           'Release': {
             'cflags': [
               '-O<(skia_release_optimization_level)',
             ],
             'defines': [ 'NDEBUG' ],
           },
         },
@@ skipping 197 matching lines @@
         # add flags here (e.g. SK_SUPPORT_LEGACY_...) needed by moz2d
       ],
     }],
 
   ], # end 'conditions'
   # The Xcode SYMROOT must be at the root. See build/common.gypi in chromium for more details
   'xcode_settings': {
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }