Experiment: enable TCMalloc on Linux by default.

chrome/chrome.gyp

Index: chrome/chrome.gyp
diff --git a/chrome/chrome.gyp b/chrome/chrome.gyp
index 4b3b096cd20cb659c0a0fef4e23d66f3fe4888bc..2da3418885a6ea95307c5106d48e641c6f1fec70 100755
--- a/chrome/chrome.gyp
+++ b/chrome/chrome.gyp
@@ -3583,6 +3583,14 @@
               'message': 'Generating manpage'
             },
           ],
+          'conditions': [
+            [ 'linux_use_tcmalloc==1', {
+                'dependencies': [
+                  '../third_party/tcmalloc/tcmalloc.gyp:tcmalloc',
+                ],
+              },
+            ],
+          ],
           'dependencies': [
             # On Linux, link the dependencies (libraries) that make up actual
             # Chromium functionality directly into the executable.