Make cr build run goma_ctl.py ensure_start before building.

tools/cr/cr/actions/ninja.py

Index: tools/cr/cr/actions/ninja.py
diff --git a/tools/cr/cr/actions/ninja.py b/tools/cr/cr/actions/ninja.py
index 404e6caea26e11360bf1b874e72c8de38f3fd697..651bca96df3a4fb780b3d04497c3af2d2cab25f4 100644
--- a/tools/cr/cr/actions/ninja.py
+++ b/tools/cr/cr/actions/ninja.py
@@ -20,7 +20,12 @@ class NinjaBuilder(cr.Builder):
       NINJA_BINARY=os.path.join('{DEPOT_TOOLS}', 'ninja'),
       NINJA_JOBS=200,
       NINJA_PROCESSORS=12,
+      NINJA_BUILD_FILE=os.path.join('{CR_BUILD_DIR}', 'build.ninja'),
       GOMA_DIR=os.path.join('{GOOGLE_CODE}', 'goma'),
+      # Don't rename to GOMA_* or Goma will complain: "unkown GOMA_ parameter".
+      NINJA_GOMA_CTL=os.path.join('{GOMA_DIR}', 'goma_ctl.py'),
+      NINJA_GOMA_CC=os.path.join('{GOMA_DIR}', 'gomacc'),
+      NINJA_GOMA_LINE='cc = {NINJA_GOMA_CC} $',
   )
   # A placeholder for the system detected configuration
   DETECTED = cr.Config('DETECTED')
@@ -30,6 +35,20 @@ class NinjaBuilder(cr.Builder):
     self._targets = []
 
   def Build(self, context, targets, arguments):
+    # Make sure Goma is started if Ninja is set to use it.
+    # This may be redundant, but it currently improves reliability.
+    try:
+      with open(context.Get('NINJA_BUILD_FILE'), 'r') as f:
+        if f.readline().rstrip('\n') == context.Get('NINJA_GOMA_LINE'):
+          # Goma is active, so make sure it's started.
+          cr.Host.ExecuteSilently(
+              context,
+              '{NINJA_GOMA_CTL}',
+              'ensure_start'
+          )
+    except IOError:
+      pass
+
     build_arguments = [target.build_target for target in targets]
     build_arguments.extend(arguments)
     cr.Host.Execute(