[Mac] Add field trial tuples to breakpad crash reports.

chrome/common/child_process_logging_mac.mm

Index: chrome/common/child_process_logging_mac.mm
===================================================================
--- chrome/common/child_process_logging_mac.mm	(revision 144791)
+++ chrome/common/child_process_logging_mac.mm	(working copy)
@@ -13,6 +13,7 @@
 #include "base/stringprintf.h"
 #include "base/sys_string_conversions.h"
 #include "base/utf_string_conversions.h"
+#include "chrome/common/metrics/experiments_helper.h"
 #include "chrome/installer/util/google_update_settings.h"
 #include "content/public/common/gpu_info.h"
 #include "googleurl/src/gurl.h"
@@ -220,8 +221,31 @@
   }
 }
 
-void SetExperimentList(const std::vector<string16>& state) {
-  // TODO(mad): Implement this.
+void SetExperimentList(const std::vector<string16>& experiments) {
+  // These should match the corresponding strings in breakpad_win.cc.
+  NSString* const kNumExperimentsKey = @"num-experiments";
+  NSString* const kExperimentChunkFormat = @"experiment-chunk-%zu";  // 1-based.
+
+  std::vector<string16> chunks;
+  experiments_helper::GenerateExperimentChunks(experiments, &chunks);
+
+  // Store up to |kMaxReportedExperimentChunks| chunks.
+  for (size_t i = 0; i < kMaxReportedExperimentChunks; ++i) {
+    NSString* key = [NSString stringWithFormat:kExperimentChunkFormat, i + 1];
+    if (i < chunks.size()) {
+      NSString* value = base::SysUTF16ToNSString(chunks[i]);
+      SetCrashKeyValue(key, value);
+    } else {
+      ClearCrashKey(key);
+    }
+  }
+
+  // Make note of the total number of experiments, which may be greater than
+  // what was able to fit in |kMaxReportedExperimentChunks|. This is useful
+  // when correlating stability with the number of experiments running
+  // simultaneously.
+  SetCrashKeyValue(kNumExperimentsKey,
+                   [NSString stringWithFormat:@"%zu", experiments.size()]);
 }
 
 void SetChannel(const std::string& channel) {