A Study of Onartuzumab in Combination With mFOLFOX6 in Participants With Metastatic HER2-Negative and MET-Positive Gastroesophageal Cancer

Participants will receive 5-fluorouracil 400 milligrams per square meter (mg/m\^2) IV bolus and then 2400 mg/m\^2 as a continuous IV infusion over 46-48 hours on Day 1 of every cycle until disease progression or at the maximum of 12 cycles, whichever occurs first.

Participants will receive folinic acid 400 mg/m\^2 IV infusion over 2 hours on Day 1 of every cycle until disease progression or at the maximum of 12 cycles, whichever occurs first.

Participants will receive onartuzumab 10 mg/kg IV infusion on Day 1 of every cycle (each cycle = 14 days) until disease progression, unacceptable toxicity, or participant or physician decision to discontinue treatment.

Participants will receive oxaliplatin 85 mg/m\^2 IV infusion over 2 hours on Day 1 of every cycle until disease progression or at the maximum of 12 cycles, whichever occurs first.

Participants will receive onartuzumab matching placebo on Day 1 of every cycle (each cycle = 14 days) until disease progression, unacceptable toxicity, or participant or physician decision to discontinue treatment.