Add unit_tests (Chrome browser unit tests) to Mac/Linux coverage....

third_party/lcov/bin/mcov

 #!/usr/bin/perl -w
 # 
 # mcov: script to convert gcov data to lcov format on Mac.
 #
 # Based on lcov (http://ltp.sourceforge.net/coverage/lcov.php)
 # Written by ajeya at google dot com.
 #
 # usage:
 # mcov --directory <base directory> --output <output file> --verbose <level>
 #
@@ skipping 234 matching lines @@
 # returns: an array with the contents of the gcov file.
 # 
 # reads the gcov file and returns the parsed contents of a gcov file
 # as an array.
 sub read_gcov_file(@) {
   my ($filename) = @_;
   my @result = ();
   my $number;
   local *INPUT;
 
-  ## TODO(ajeya): Exit more gracefully here.
-  open(INPUT, $filename) or die("ERROR: cannot read $filename!\n");
+  if (!open(INPUT, $filename)) {
+    warn("WARNING: cannot read $filename!\n");
+    return @result;
+  }
   
   # Parse gcov output and populate the array
   my @lines = <INPUT>;
   foreach my $line (@lines) {
     chomp($line);
     if ($line =~ /^\s*([^:]+):\s*(\d+?):(.*)$/) {
       # <exec count>:<line number>:<source code>
       
       if ($1 eq "-") {
         # Uninstrumented line
@@ skipping 13 matching lines @@
         push(@result, 1);
         push(@result, $number);
         push(@result, $3);
         push(@result, $2);
       }  
     }
   }
   close(INPUT);
   return @result;
 }